Graphite film and method for producing graphite film

ABSTRACT

It is possible to obtain a graphite film with its shape controlled, by performing a sag controlling step of controlling temperatures of a polymer film at both widthwise ends and a temperature of the polymer film in a widthwise middle portion within a temperature range from a starting temperature of thermal decomposition of the polymer film to a sag controlling temperature of the polymer film.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Divisional of co-pending application Ser. No.14/240,221 filed on Mar. 24, 2014, which is a National Phase of PCTInternational Application No. PCT/JP2012/070890 filed on Aug. 17, 2012,which claims priority under 35 U.S.C. § 119(a) to Patent Application No.2011-182654 filed in Japan on Aug. 24, 2011, Patent Application No.2011-182655 filed in Japan on Aug. 24, 2011, and Patent Application No.2011-262458 filed in Japan on Nov. 30, 2011. All of the aboveapplications are hereby expressly incorporated by reference into thepresent application.

TECHNICAL FIELD

The present invention relates to a graphite film and a method forproducing a graphite film.

BACKGROUND ART

Graphite films are classified into: graphite films (also referred to as“natural graphite sheets”) produced by an expanding method; and graphitefilms (also referred to as “fired polymer-based graphite film”) producedby polymer thermal decomposition.

Fired Polymer-based graphite films are used as heat dissipationcomponents for dissipating heat from components that generate heat,e.g., for semiconductor elements that are mounted in various electronicor electric apparatuses such as computers. As an example of the firedpolymer-based graphite film, a graphite film having an excellentmechanical strength and having flexibility is disclosed in PatentLiterature 1. According to Patent Literature 1, such a graphite film isobtained by raising the temperature of a polymer film of 75 μm inthickness up to 1000° C. in a nitrogen gas, heating a carbonized filmthus obtained up to 3000° C. in an atmosphere of argon, and thensubjecting a graphitized film thus obtained to a rolling process.

In addition, graphite films have the characteristics of having a lowertearing strength, as compared to typical plastic films and other films.Particularly, in the case of the fired polymer-based graphite films,their molecular structures are such that the molecules of graphite aremore uniformly oriented in parallel to its planar direction. Thus, thefired polymer-based graphite films have the tendency to show lowresistance to shearing stress, i.e., the tendency to show low tearingstrength (average tearing force).

Patent Literature 2 discloses a method for reinforcing a pullingstrength of a flexible graphite sheet (equivalent to a natural graphitesheet). According to this method, a flexible graphite sheet (naturalgraphite sheet) and a thin film of thermoplastic polymer having a givensoftening temperature are laminated to each other as they are suppliedbetween temperature-controlled two calender rolls.

Further, heat dissipation components are used to dissipate heat fromcomponents that generate heat, e.g., for semiconductor elements that aremounted in various electronic or electric apparatuses such as computers.When a graphite film is used for large products among the heatdissipation components, the graphite film is preferably a long andlarge-area graphite film wound in roll form and made from a polymerfilm. Studies for producing such a graphite film have been made.

For example, there has been proposed a method of heat-treating a 30 mwide and 250 mm long polymer film wound around a carbonaceouscylindrical inner core having an outer diameter of 150 mm. This methodmakes it possible to obtain a long and large-area graphite film whosecylindrical hysteresis can easily be extended (Patent Literature 3).

CITATION LIST Patent Literatures

Patent Literature 1

Japanese Patent Application Publication, Tokukaihei, No. 3-75211 A

Patent Literature 2

Japanese Patent Application Publication, Tokukaihei, No. 6-24872 A

Patent Literature 3

Japanese Patent Application Publication, Tokukai, No. 2006-327907 A

SUMMARY OF INVENTION Technical Problem

However, the method described in Patent Literature 1 had difficulty incontrolling sagging of a fired polymer-based graphite film. Inparticular, there is a tendency that it is more difficult to controlsagging of a fired polymer-based graphite film having a longer length(for example, a length of not less than 700 mm) than to control saggingof a fired polymer-based graphite film having a shorter length.

Further, in a case where the method described in Patent Literature 2 isapplied to a fired polymer-based graphite film, the firedpolymer-derived graphite film is torn at the edges thereof, as shown inFIG. 1, before supplied between the two rolls. This results in thefailure to laminate with a thin film of thermoplastic polymer.

In addition, graphite films can be processed with, e.g., self-adhesivematerial layers, insulating films, and other protective films intocomposite products. In this case, as in the above case, graphite filmssuffered from a defect such as tearing. Such a defect tends to moresignificantly occur on a fired polymer-based graphite film having alonger length (for example, a length of not less than 700 mm) than on afired polymer-based graphite film having a shorter length.

Further, the conventional method as described in Patent Literature 3caused a deep sag Zgs as shown in FIG. 23. It was impossible to producea graphite film excellent in flatness by suppressing such a deep sag.Such a conventional graphite film had the problem that it tends tosuffer from a defect when laminated with an adhesive tape such as acopper foil tape (see FIG. 24).

Solution to Problem

The present invention encompasses the following inventions:

(1) A method for producing a graphite film, comprising: a sagcontrolling step of controlling (i) temperatures of a polymer film atboth widthwise ends and (ii) a temperature of the polymer film in awidthwise middle portion within a temperature range from a startingtemperature of thermal decomposition of the polymer film to a sagcontrolling temperature of the polymer film; and a step of treating thefilm obtained in the sag controlling step with heat at a temperature of2000° C. or higher after the sag controlling step.

(2) The method according to (1), wherein the sag controlling stepcomprises treating the polymer film with heat so that the temperatures(i) are higher than the temperature (ii) within the temperature rangefrom the starting temperature of thermal decomposition of the polymerfilm to the sag controlling temperature of the polymer film and so thata temperature gradient over an area extending from the both widthwiseends of the polymer film toward the widthwise middle portion of thepolymer film is not less than 2.5° C./m, and the film obtained in thesag controlling step is treated with heat at a temperature of 2000° C.or higher after the sag controlling step.

(3) The method according to (2), wherein in the sag controlling step,the polymer film is treated with heat while being moved through a heattreatment apparatus.

(4) The method according to (2) or (3), wherein the sag controlling steptreats the polymer film with heat under a condition that the temperaturegradient over an area extending from the both widthwise ends of thepolymer film toward the widthwise middle portion of the polymer film isnot less than 2.5° C./m and not more than 100° C./m.

(5) The method according to any one of (2) through (4), wherein atemperature gradient over an area extending from one of the bothwidthwise ends of the polymer film toward the widthwise middle portionof the polymer film is identical to a temperature gradient over an areaextending from the other of the both widthwise ends of the polymer filmtoward the widthwise middle portion of the polymer film.

(6) The method according to any one of (2) through (4), wherein atemperature gradient over an area extending from one of the bothwidthwise ends of the polymer film toward the widthwise middle portionof the polymer film is different from a temperature gradient over anarea extending from the other of the both widthwise ends of the polymerfilm toward the widthwise middle portion of the polymer film.

(7) A graphite film having a sag resulting from different lengthwiselengths of the graphite film across a width of the graphite film, thesag being formed in a shape such that areas extending from a widthwisemiddle portion of the graphite film toward both widthwise ends of thegraphite film are bilaterally symmetric with respect to the widthwisemiddle portion of the graphite film.

(8) A graphite film having sag resulting from different lengthwiselengths of the graphite film across a width of the graphite film, thesag being formed in a shape such that areas extending from a widthwisemiddle portion of the graphite film toward both widthwise ends of thegraphite film are bilaterally asymmetric with respect to the widthwisemiddle portion of the graphite film.

(9) The method according to (1), wherein the sag controlling stepcomprises treating the polymer film with heat so that the temperatures(i) are lower than the temperature (ii) and so that a temperaturegradient over an area extending from the both widthwise ends of thepolymer film toward the widthwise middle portion of the polymer film isnot more than −2.5° C./m.

(10) The method according to (9), wherein in the sag controlling step,the polymer film is treated with heat so that a temperature gradientover an area extending from the both widthwise ends of the polymer filmtoward the widthwise middle portion of the polymer film is not less than−100° C./m.

(11) A graphite film having a sag resulting from different lengthwiselengths of the graphite film across a width of the graphite film, thesag lying in a widthwise middle portion of the graphite film.

(12) The graphite film according to (11), wherein

a b-value of the sag in the widthwise middle portion of the graphitefilm is not less than 5 mm.

(13) The method according to (1), wherein the sag controlling steptreats the polymer film with heat so that a temperature gradient over anarea extending from the both widthwise ends of the polymer film towardthe widthwise middle portion of the polymer film is not less than −2.4°C./m and not more than 2.4° C./m.

(14) A graphite film having a sag of 20.0 mm or less as determined by amethod of film windability evaluation in accordance with JIS C2151.

(15) A graphite film having a sag of 4.9 mm or less as determined by amethod of film windability evaluation in accordance with JIS C2151.

(16) The method according to (1), wherein in the sag controlling step,the polymer film is treated with heat so that Temperature A≥TemperatureB≥Temperature C and Temperature A≠Temperature C (where Temperature A isa temperature of the polymer film at one of the both widthwise ends,Temperature B is a temperature of the polymer film in the widthwisemiddle portion, and Temperature C is a temperature of the polymer filmat the other of the both widthwise ends) and so that a temperaturegradient from Temperature A to Temperature C is not less than 2.5° C./m.

(17) A graphite film having a sag resulting from different lengthwiselengths of the graphite film across a width of the graphite film, thesag lying at one widthwise end of the graphite film.

(18) The graphite film according to (17), wherein the graphite film hascamber of not less than 11 mm.

(19) The method according to any one of (1), (9), (10), (13), and (16),wherein in the sag controlling step, the polymer film is treated withheat while being moved through a heat treatment apparatus.

(20) A method for producing a graphite film, comprising: a straighteningprocess step of treating a raw graphite film with heat up to atemperature of 2000° C. or higher while applying a pressure to the rawgraphite film, wherein the raw graphite film is treated with heat in astate such that the raw graphite film is wound around an inner corehaving diameter accuracy of less than 0.0426° C.

(21) The method according to (20), wherein the raw graphite film asemployed in the straightening process step is obtained by treating apolymer film with heat of 2000° C. or higher, and the raw graphite filmis cooled at least once to a temperature of lower than 2000° C. beforesubjected to the straightening process step.

(22) The method according to (20) or (21), wherein the diameter accuracyof the inner core is less than 0.0027° C.

Advantageous Effects of Invention

According to a graphite film or a method for producing a graphite filmin accordance with the above (1), (9) through (13), and (15) through(19), it is possible to control sagging of a graphite film.

Further, according to a graphite film or a method for producing agraphite film in accordance with the above (2) through (8), it ispossible to control sagging of a graphite film, thereby obtaining agraphite film that resists tearing.

Still further, according to a graphite film or a method for producing agraphite film in accordance with the above (14) and (20) through (22),it is possible to obtain a graphite film excellent in flatness.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a photograph showing an appearance of a tear of a graphitefilm.

FIG. 2 is a schematic view showing sag measurement described in JISC2151.

FIG. 3 illustrates a mechanism for forming a sag.

FIG. 4 is photographs each showing a graphite film having a sag.

FIG. 5 is an explanatory view of the definitions of ends of a film and amiddle portion of the film.

FIG. 6 is a schematic view showing a sag controlling step carried out bya sheet batch method.

FIG. 7 is a schematic view showing a sag controlling step carried out bya cylindrical batch method.

FIG. 8 is a schematic view showing a sag controlling step carried out bya continuous long film processing method.

FIG. 9 is a schematic view showing a a-value.

FIG. 10 is a schematic view showing a b-value.

FIG. 11 is a schematic view showing camber measurement described in JISC2151.

FIG. 12 is a schematic view of a test of resistance to tearing.

FIG. 13 is a schematic view of a test of lamination property.

FIG. 14 is an explanatory view of an angle formed by a line connecting(the starting point of contact between the first roll and the graphitefilm) and (the center point of the first roll) and a line connecting(the center point of the first roll) and (the point of contact betweenthe first roll and the second roll).

FIG. 15 is a photograph showing an appearance of laminating wrinkles.

FIG. 16 shows how a film is set in the carbonization step and in thegraphitization step in Examples and Comparative Examples.

FIG. 17 is a photograph showing an appearance of folding wrinkles of agraphite film which wrinkles occur during the rolling process.

FIG. 18 is a schematic view showing a sag controlling step carried outby a sheet batch method.

FIG. 19 is a schematic view showing a sag controlling step carried outby a cylindrical batch method.

FIG. 20 is a schematic view showing a sag controlling step carried outby a continuous long film processing method.

FIG. 21 is a photograph showing an appearance of laminating wrinkles.

FIG. 22 is a view schematically showing a rolling process.

FIG. 23 is a view showing one example of sag of a graphite film.

FIG. 24 is a photograph showing an appearance of laminating wrinkleswith respect to copper foil tape.

FIG. 25 is a photograph showing an appearance of winding deviation of agraphite film.

FIG. 26 is a view showing a method of applying a load to the surface ofa raw graphite film in sheet form.

FIG. 27 shows a method of pushing wide a raw graphite film by utilizingthermal expansion of an inner core.

FIG. 28 shows one example of a rewinding step.

FIG. 29 shows a jig used in the carbonization process according to thethird embodiment of the present invention.

FIG. 30 is a container for performing a graphitization step in such astate that a film is arranged transversely.

FIG. 31 is a schematic view showing sag measurement described in JISC2151.

FIG. 32 shows an irreversible elongation of a film in a graphitizationstep.

FIG. 33 shows points from which samples of a graphite film are collectedfor the measurement of thermal diffusivities of the samples.

FIG. 34 is a schematic view of a test of laminating test.

FIG. 35 shows tears of a graphite film.

FIG. 36 is a view showing sags of the graphite films before and afterhaving been subjected to the straightening process in Example 1C.

FIG. 37 shows an example of use of a graphite film according to thethird embodiment of the present invention.

FIG. 38 is a view showing the straightening process with use of anexpendable inner core.

FIG. 39 shows a jig for straightening a film in sheet form by utilizinga difference in thermal expansion.

FIG. 40 is a view of a graphite film having bilaterally asymmetric sag.

FIG. 41 is a view of a graphite film having bilaterally symmetric sag.

FIG. 42 is a view of a graphite film having a sag in a middle portionthereof.

FIG. 43 is a view of a graphite film having a sag of not more than 4.9mm.

FIG. 44 is a view of a graphite film having a sag at one end thereof.

FIG. 45 is a view of a graphite film having a sag of not more than 20mm.

DESCRIPTION OF EMBODIMENTS

The present invention relates to a graphite film and a method forproducing a graphite film. Specifically, the present invention relatesto, for example, a graphite film with controlled sag and a method forproducing a graphite film in which method sag of the graphite film iscontrolled. In another embodiment, the present invention relates to agraphite film having a specific sag and a method for producing agraphite film in which method a specific sag occurs on the graphitefilm. In still another embodiment, a graphite film improved in flatness,a method for producing a graphite film improved in flatness, and amethod for improving flatness of a graphite film.

The following will describe embodiments of the present invention. All ofthe academic literatures and patent literatures listed herein areincorporated by reference herein. Unless otherwise specified herein, theexpression indicating a numerical range, i.e., “A to B” means “not lessthan A (including A and more than A) and not more than B (including Band less than B)”, and “%” and “parts” means “% by mass” and “parts bymass”, respectively.

(1. First Embodiment of the Present Invention)

“Sag” of a graphite film refers to “distortion” that appears on thefilm, as determined by a method of film windability evaluation inaccordance with JIS C2151. A film in a certain length is wound off andplaced between two parallel sticks in a direction at right angles to thesticks under prescribed conditions, as illustrated in FIG. 2. Then, adeviation from a uniform suspended line is measured. A film having “sag”can be confirmed as follows. When the film is stretched, part of thefilm sags to a height lower than a normal height of the part of thefilm. As illustrated in FIG. 3, the sag appears due to differencesbetween the lengths of a film along a lengthwise direction 32 (alsoreferred to as “long side direction” and “MD direction” in the presentapplication) across a widthwise direction 31 (also referred to as “shortside direction” and “TD direction” in the present application) of thefilm. For example, the sag occurs due to differences between a length 33of a middle portion of the film and respective lengths 34 and 36 of bothends of the film.

The inventors of the present application found that there is acorrelation between such a sag and the ease of tearing of a graphitefilm. For example, a graphite film 41 having a sag in a widthwise middleportion thereof as shown in FIG. 4 is more likely to tear when tensionedin a lengthwise direction of the film. This is because load tends toconcentrate on the ends of the graphite film 41. Also, a graphite film42 having a sag of less than 5 mm can tear because even a slightdeviation of a shaft causes concentration of load on the ends of thegraphite film 42. Meanwhile, a graphite film 43 having sags at bothwidthwise ends thereof as shown in FIG. 4 is hardly torn because load isless likely to be applied to the ends of the graphite film 43 (a causeof tearing is less likely to occur).

The first embodiment of the present invention relates to a productionmethod for producing a graphite film having a sag. In the firstembodiment of the present invention, the inventors of the presentinvention found that in order to obtain a sag of a graphite film, it isimportant to treat a polymer film with heat under a condition such thatthe temperatures of the polymer film at both widthwise ends are higherthan the temperature of the polymer film in a widthwise middle portionwithin the temperature range from a starting temperature of thermaldecomposition of the polymer film to a sag controlling temperature ofthe polymer film and a condition such that a temperature gradient overan area extending from the both widthwise ends of the polymer filmtoward the widthwise middle portion of the polymer film is not less than2.5° C./m (hereinafter, such a heat treatment step is referred to as“sag controlling step”). That is, a graphite film of the firstembodiment of the present invention is obtained by subjecting a polymerfilm to the sag controlling step and then treating the film obtained inthe sag controlling step with heat at a temperature of 2000° C. orhigher. The first embodiment of the present invention is an embodimentto obtain a tear-resistant graphite film having sags at ends thereof, bycontrolling sag of the graphite film by subjecting the polymer film to aspecial heat treatment at a temperature in a particular temperaturerange in an early stage of decomposition of the polymer film.

A mechanism of the development of the effect of the sag controlling stepaccording to the first embodiment of the present invention is asfollows. First, in the early stage of thermal decomposition of a polymerfilm, the polymer film is treated with heat at temperatures such thatboth widthwise ends of the polymer film are relatively higher intemperature than a widthwise middle portion of the polymer film. Thepolymer film thus given a thermal hysteresis which varies across thewidth varies in progress of graphitization of the polymer film in thegraphitization step that follows the carbonization step (i.e. varies indegree of orientation of graphite crystallites). This results in agraphite film such that lengthwise lengths of the graphite film at bothends are longer than a lengthwise length of the graphite film in themiddle portion. Thus, when such a graphite film is observed in thewidthwise direction thereof, the appearance of sags of the graphite filmis confirmed at the both ends of the graphite film, wherein thelengthwise lengths of the graphite film at the both ends are longer thanthe length of the graphite film at their peripheral portions.

Examples of a production method for obtaining a graphite film from atypical polymer film encompasses a method including: a carbonizationstep of generally heating the polymer film at a temperature of up toaround 1000° C.; and a graphitization step of heating a carbonized filmthus obtained in the carbonization step at a temperature of 2600° C. orhigher. The sag controlling step according to the first embodiment ofthe present invention serves to control a widthwise temperaturedistribution of a polymer film in the temperature range in acomparatively early stage of the carbonization step.

Examples of a method for producing a graphite film that involves theexecution of the sag controlling step according to the first embodimentof the present invention encompass: a method of performing the sagcontrolling step and a temperature decreasing step in succession andthen performing the carbonization step and the graphitization step; anda method of performing both the sag controlling step and thecarbonization step in one process (performing the sag controlling stepand subsequently performing the carbonization step, without atemperature decrease intervening between the sag controlling step andthe carbonization step) and then performing the graphitization step.

<Definitions of Ends and Middle Portions of Polymer Film and of GraphiteFilm>

The ends of both a polymer film and a graphite film are each defined asedge portions of both the polymer film and the graphite film which edgeportions are parallel to the lengthwise direction thereof when each ofthe films is spread out, as indicated by reference numeral 52 in FIG. 5.Further, the middle portions of both the polymer film and the graphitefilm are each defined as a center of the film, as indicated by referencenumeral 51 in FIG. 5, which center is located at an equal distance fromboth of the ends of the film.

<Widthwise Temperature Gradient in the Sag Controlling Step>

A graphite film that is sagging at both ends of the graphite film and ishardly torn is obtained by (a) treating a polymer film with heat attemperatures such that temperatures of the polymer film at both ends arerelatively higher than a temperature of the polymer film in the middleportion within a temperature range from a starting temperature ofthermal decomposition to a sag controlling temperature and then (b)executing the graphitization step. In this regard, a graphite filmsagging at both ends can also be obtained by arbitrarily setting thewidthwise temperature gradient and/or temperature distribution of thefilm over an area extending from both ends of the film to the middleportion of the film in a temperature range over the sag controllingtemperature.

A temperature gradient over an area extending from the ends of a film tothe middle portion of the film according to the first embodiment of thepresent invention is expressed, with use of respective temperatures ofan end and a middle portion on a given straight line perpendicular tothe lengthwise direction of the film and the width of the film as shownin FIG. 5, by the following equation:Temperature Gradient=(Temperature of Film at Both Ends−Temperature ofFilm in Middle Portion)/(Width of Film/2)×100.

The temperatures of the film at the both ends and in the middle portionacross a given width are values measured at the same time. According tothe first embodiment of the present invention, a temperature gradientover an area extending from the both ends to the middle portion(temperature gradient over an area extending from an end 1 to the middleportion and temperature gradient over an area extending from an end 2(the other end different from the end 1) to the middle portion) is notless than 2.5° C., preferably not less than 5° C., and more preferablynot less than 10° C. An upper limit of the temperature gradients fromthe both ends to the middle portion, which is not particularly limited,is preferably not more than 100° C., more preferably not more than 50°C., or even more preferably not more than 25° C. It is preferable thateach of the temperature gradients over an area extending from one of theboth ends to the middle portion and over an area extending from theother of the both widthwise ends to the widthwise middle portion is notless than 2.5° C./m, because it realizes a tear-resistant graphite filmsufficiently sagging at the both ends thereof. Further, it is preferablethat each of the temperature gradients over an area extending from oneof the both ends to the middle portion and over an area extending fromthe other of the both widthwise ends to the widthwise middle portion isnot more than 100° C., because it realizes a graphite film so adequatelysagging at the both ends thereof as to obtain excellent laminationproperty when laminated with other medium in film form.

According to the first embodiment of the present invention, it ispossible to obtain a bilaterally symmetric graphite film when thetemperature gradient over an area extending from the end 1 to the middleportion and the temperature gradient over an area extending from the end2 to the middle portion are the same as each other. Meanwhile, it ispossible to obtain a bilaterally asymmetric graphite film when thetemperature gradient over an area extending from the end 1 to the middleportion and the temperature gradient over an area extending from the end2 to the middle portion are different from each other.

<Decomposition Reaction and Weight Loss Rate of Polymer Film in the SagControlling Step>

As a result of heat-treating a polymer film, substances not involvingformation of a graphite skeleton, e.g., carbon, oxygen, hydrogen, and/ornitrogen are sequentially discharged as components of carbon dioxidegas, water, hydrogen gas, nitrogen gas, and/or tar, as the temperatureof the heat treatment increases. As the decomposition of the polymerfilm progresses, the polymer film becomes blackened and vitrified. Theterm “weight loss rate of a polymer film during the sag controllingstep” (also referred to as “weight loss rate”) can be calculated byusing an initial weight (a weight of the polymer film at 23° C. and 50%humidity before heat treatment is started) of the polymer film, whichserves as the starting material, and a weight of the polymer filmimmediately after the sag controlling step, according to the followingequation:Weight loss rate (%)=[(Initial weight of polymer film−Weight of polymerfilm immediately after the sag controlling step)/Initial weight ofpolymer film]×100.

It should be noted that the weight of the polymer film is the weight asmeasured in an environment of 23° C. and 50% humidity after the polymerfilm has been allowed to stand for 24 hours in the same environment. Thesame applies to all of the embodiments and Examples.

<Method for Measuring Temperature of Film>

The first embodiment of the present invention makes it possible tocontrol sag by treating a polymer film with heat while giving a desiredtemperature gradient across the width of the polymer film within atemperature range from a starting temperature of thermal decompositionof the polymer film to a sag controlling temperature of the polymerfilm.

The starting temperature of thermal decomposition of the polymer filmand the sag controlling temperature are actual temperatures of thewidthwise middle portion of the polymer film itself being heat-treated.The actual temperature of the polymer film itself can be measured byusing a 0.5 mm-diameter sheathed type K thermocouple brought intocontact with the polymer film.

Note that in the first embodiment of the present invention, there are noparticular limitations to temperature ranges in any steps other than thesag controlling step, more specifically, a condition for heat treatmentperformed at a temperature lower than the starting temperature ofthermal decomposition of the polymer film and a condition for heattreatment performed at a temperature higher than the sag controllingtemperature after the sag controlling step is once performed.

Further, the sag controlling step may be followed by cooling to roomtemperature, before the subsequent heat treatment steps (thecarbonization step and the graphitization step) are performed.Alternatively, the sag controlling step may be followed by a subsequentheat treatment, without a temperature decrease intervening between thesag controlling step and the heat treatment. The carbonization step canbe omitted provided that the subsequent heat treatment is performed at atemperature of preferably up to not less than 700° C., more preferablyup to not less than 800° C., or even more preferably up to not less than900° C.

<Starting Temperature of Thermal Decomposition of Polymer Film and SagControlling Temperature>

According to the first embodiment of the present invention, the startingtemperature of thermal decomposition of a polymer film is defined as atemperature at which a polymer film, as a result of heat treatment,loses 1.0% of its initial weight which has been measured at roomtemperature (23° C., 50% humidity) before the heat treatment is started.More specifically, the starting temperature of thermal decomposition ofa polymer film according to the first embodiment of the presentinvention is a temperature at which a 10 mg sample of the polymer filmloses 1.0% of its weight as a result of heat treatment performed at atemperature rise rate of 10° C./min from room temperature (23° C.) to1000° C. under a flowing nitrogen atmosphere (200 mL per minute) bymeans of a thermal analysis system EXSTAR6000 and a thermogravimetricapparatus TG/DTA 220U (both manufactured by SII Nanotechnology Inc.).The starting temperature of thermal decomposition according to the firstembodiment of the present invention is specifically measured as follows.That is, a 10 mg sample of a polymer film is heat-treated at atemperature rise rate of 10° C./min from room temperature (23° C.) to1000° C. under a flowing nitrogen atmosphere (200 mL per minute) bymeans of a thermal analysis system EXSTAR6000 and a thermogravimetricapparatus TG/DTA 220U (both manufactured by SII Nanotechnology Inc.). Atemperature at which the polymer film loses 1.0% of its weight isdefined as the starting temperature of thermal decomposition of thepolymer film.

The sag controlling temperature according to the first embodiment of thepresent invention is a temperature at which a polymer film, as a resultof heat treatment, loses not less than 1.1%, preferably not less than1.2%, more preferably not less than 2.8%, even more preferably not lessthan 10.0%, especially preferably not less than 15.0%, or mostpreferably 20.0%, of its initial weight which has been measured at roomtemperature (23° C., 50% humidity) before the heat treatment is started.Such a temperature is determined based on a result of the measurement ofa weight loss of a polymer film heat-treated at a temperature rise rateof 10° C./min from room temperature (23° C.) to 1000° C. under a flowingnitrogen atmosphere (200 mL per minute) by means of a thermal analysissystem EXSTAR6000 and a thermogravimetric apparatus TG/DTA 220U (bothmanufactured by SII Nanotechnology Inc.). The sag controllingtemperature which causes a weight loss rate of not less than 1.1%enables developing the effect of sag control. Further, a higher settingof the sag control enables enhancing the effect of sag control. In acase where the sag controlling temperature is a temperature at which aweight loss rate of a polymer film does not exceed 20.0% (upper limitvalue to the sag control), the sag controlling step may be asingle-stage sag controlling step or a multi-stage sag controlling step.Alternatively, the sag controlling step may be performed two or moretimes. By all these sag controlling steps, sag amplification can berealized. In such a case, the temperatures of widthwise ends of a filmare set higher than the temperature of a widthwise middle portion of thefilm until the sag controlling temperature reaches a temperature atwhich the weight loss rate of the film exceeds 20%. In a temperaturerange in which a weight loss rate exceeds 20.0%, there is no differencebetween a sag of a graphite film obtained as a final product under thecondition that the temperatures of widthwise ends of a film are sethigher than the temperature of a widthwise middle portion of the filmand a sag of a graphite film obtained as a final product without such acondition.

A temperature at which a polymer film shows a weight loss rate of 20%,as the most preferable sag controlling temperature according to thefirst embodiment of the present invention, is specifically measured asfollows. That is, a weight loss of a 10 mg sample of a polymer film as aresult of heat treatment performed at a temperature rise rate of 10° C.per minute from room temperature (23° C.) to 1000° C. under a flowingnitrogen atmosphere (200 mL per minute) is measured by means of athermal analysis system EXSTAR6000 and a thermogravimetric apparatusTG/DTA 220U (both manufactured by SII Nanotechnology Inc.). Based on aresult of the measurement, a temperature at which the polymer filmshowed 20% weight loss is determined as the sag controlling temperature.Similarly, a temperature at which a polymer film shows a weight lossrate of 1.1%, which temperature is a lower limit to the sag controllingtemperature, is determined as follows. That is, a weight loss of a 10 mgsample of a polymer film as a result of heat treatment performed at atemperature rise rate of 10° C. per minute from room temperature (23°C.) to 1000° C. under a flowing nitrogen atmosphere (200 mL per minute)is measured by means of a thermal analysis system EXSTAR6000 and athermogravimetric apparatus TG/DTA 220U (both manufactured by SIINanotechnology Inc.). Based on a result of the measurement, atemperature at which the polymer film showed 1.1% weight loss isdetermined as the temperature at which the polymer film shows a weightloss rate of 1.1%.

In the case where the sag controlling step is followed by a temperaturedecrease before another step is performed, the handleability of the filmobtained through the sag controlling step is important. In that case,when the sag controlling temperature is set so that the polymer filmshows a weight loss rate of preferably not more than 20.0%, morepreferably not more than 15.0%, even more preferably not more than10.0%, or especially preferably not more than 2.8%, the polymer film isnot completely carbonized and therefore has the nature of a polymerremained therein, thus being hardly cracked and having goodhandleability. Further, in such the case, an amount that the polymerfilm shrinks is small, with the result that the polymer film hardly getswrinkles.

<Starting Temperature of Thermal Decomposition of Polymer Film as Usedin Examples of First Embodiment of the Present Invention and SagControlling Temperature of the Polymer Film>

For polyimide films as used in Examples of the first embodiment of thepresent invention (polyimide films manufactured by Kaneka Corporation:Apical AH of 75 μm in thickness; and Apical NPI of 75 μm in thickness),the starting temperature of thermal decomposition of these polyimidefilms and the sag controlling temperature thereof are as follows. Thestarting temperature of thermal decomposition is 500° C. (weight lossrate of 1.0%). The sag controlling temperature is 520° C. (weight lossrate of 1.1%) or more, preferably 550° C. (weight loss rate of 1.2%) ormore, more preferably 580° C. (weight loss rate of 2.8%) or more, evenmore preferably 600° C. (weight loss rate of 10.0%) or more, especiallypreferably 630° C. (weight loss rate of 15.0%) or more, or mostpreferably 655° C. (weight loss rate of 20.0%) or more. When the sagcontrolling temperature is 520° C. or more, it is possible to obtain theeffect attained by the sag controlling step. The higher the sagcontrolling temperature, the further the effect attained by the sagcontrolling step is enhanced. In a case where the sag controllingtemperature does not exceed 655° C. (upper limit to the sag control),the sag controlling step may be a single-stage sag controlling step or amulti-stage sag controlling step. Alternatively, the sag controllingstep may be performed two or more times. By all these sag controllingsteps, sag amplification can be realized. In this case, the temperaturesof widthwise ends of a film are set higher than the temperature of awidthwise middle portion of the film until the sag controllingtemperature reaches a temperature exceeding 655° C. In a temperaturerange exceeding 655° C., there is no difference between a sag of agraphite film obtained as a final product under the condition that thetemperatures of widthwise ends of a film are set higher than thetemperature of a widthwise middle portion of the film and a sag of agraphite film obtained as a final product without such a condition.

<Method for Performing the Sag Controlling Step>

In the sag controlling step, any method may be employed, withoutparticular limitation, as a method of treating a polymer film with heatwhile giving a temperature gradient to the polymer film across the widthof the polymer film. One example of such a method is a method of holdinga sheet-type polymer film (which means “one or more polymer films insheet form”) by inserting the polymer film into a graphite jig within aheat treatment apparatus, and then heat-treating the polymer filmbatchwise (sheet batch method), as shown in FIG. 6. The other example isa method of holding a polymer film by wrapping around a graphitecylindrical container, and then heating the polymer film batchwise withheat (cylindrical batch method), as shown in FIG. 7. Another example isa method of subjecting a long polymer film to heat treatment whilecontinuously supplying the long polymer film into the heat treatmentapparatus (continuous processing method or continuous long filmprocessing method), as shown in FIG. 8. Note that the widthwisedirection according to the first embodiment of the present invention isa direction along which a difference in temperature is given in the sagcontrolling step. In a case where a long film is to be employed, thewidthwise direction thereof, which is not particularly limited, ispreferably a short side of the film (a direction vertical to thelengthwise direction), from a viewpoint of enabling a furtherdevelopment of the effect of sagging. From a similar viewpoint, in acase where a continuous long film processing method is to be employed,it is preferable that the widthwise direction is preferably a TDdirection rather than a MD direction.

In a case where the sag controlling step is performed in the sheet batchmethod, widthwise temperature control of a polymer film is carried outby increasing temperatures of the polymer film within a temperaturerange from the starting temperature of thermal decomposition of thepolymer film to the sag controlling temperature thereof in such a statethat a difference in temperature is given between the widthwise ends ofthe polymer film and the middle portion thereof (see one example ofwidthwise temperature distribution of a polymer film shown in FIG. 6).In this case, the temperature range from the starting temperature ofthermal decomposition of the polymer film to the sag controllingtemperature needs to satisfy a condition such that the temperatures ofthe polymer film at the both widthwise ends are set higher than thetemperature of the polymer film in the widthwise middle portion and acondition that a temperature gradient over an area extending from theboth widthwise ends to the widthwise middle portion of the polymer filmis not less than 2.5° C./m. Particularly, it is preferable that, at thesag controlling temperature, temperature measurement points in the sagcontrolling step satisfy such a condition that the temperature gradientover an area extending from the both widthwise ends of the polymer filmto the widthwise middle portion of the polymer film is not less than2.5° C./m. Further, it is preferable that at least 70% of thetemperature measurement points in the sag controlling step satisfy sucha condition that the temperature gradient over an area extending fromthe both widthwise ends of the polymer film to the widthwise middleportion of the polymer film is not less than 2.5° C./m. Although it isparticularly preferable that the difference in temperature constantlyfall within a certain range, the difference in temperature may varywithin a range yielding the effect of the first embodiment of thepresent invention.

The measurement of temperatures of a polymer film is performed, as shownin FIG. 6, by means of 0.5 mm-diameter sheathed type K thermocouplesplaced in contact with the both ends of the polymer film and the middleportion of the polymer film at intervals of 100 mm along the lengthwisedirection of the polymer film.

In the temperature range from the starting temperature of thermaldecomposition to the sag controlling temperature, time-varying changesin temperature at the ends of the film and in the middle portion of thefilm are also measured at 30° C. intervals (at the points of time, 500°C., 530° C., 560° C., and 580° C., in a case where the startingtemperature of thermal decomposition in the widthwise middle portion ofthe film and the sag controlling temperature are 500° C. and 580° C.,respectively) starting from the starting temperature of the widthwisemiddle portion of the film. Such measurement is performed to confirmthat at least one of the four measured temperatures, preferably allthese four measured temperatures, satisfy such a condition that thetemperature gradient over an area extending from the both ends to themiddle portion is not less than 2.5° C./m.

As in the case where the sag controlling step is performed in the sheetbatch method, in a case where the sag controlling step is performed inthe cylindrical batch method, widthwise temperature control of a polymerfilm is carried out by increasing temperatures of the polymer filmwithin a temperature range from the starting temperature of thermaldecomposition of the polymer film to the sag controlling temperaturethereof in such a state that a difference in temperature is givenbetween the widthwise ends of the polymer film and the middle portionthereof (see one example of widthwise temperature distribution of apolymer film shown in FIG. 7). In this case, the temperature range fromthe starting temperature of thermal decomposition of the polymer film tothe sag controlling temperature thereof needs to satisfy a conditionsuch that the temperatures of the polymer film at the both widthwiseends are set higher than the temperature of the polymer film in thewidthwise middle portion and a condition such that a temperaturegradient over an area extending from the both widthwise ends of thepolymer film to the widthwise middle portion of the polymer film is notless than 2.5° C./m. Particularly, it is preferable that, at the sagcontrolling temperature, temperature measurement points in the sagcontrolling step satisfy such a condition that the temperature gradientover an area extending from the both widthwise ends of the polymer filmto the widthwise middle portion of the polymer film is not less than2.5° C./m. Further, it is preferable that at least 70% of thetemperature measurement points in the sag controlling step satisfy sucha condition that the temperature gradient over an area extending fromthe both widthwise ends to the widthwise middle portion of the polymerfilm is not less than 2.5° C./m. Although it is particularly preferablethat the difference in temperature constantly fall within a certainrange, the difference in temperature may vary within a range yieldingthe effect of the first embodiment of the present invention.

The measurement of temperatures of a polymer film is performed, as shownin FIG. 7, by means of 0.5 mm-diameter sheathed type K thermocouplesplaced in contact with the both ends of the polymer film and the middleportion of the polymer film at the respective points circumferentiallyprovided at 90-degree intervals.

In the temperature range from the starting temperature of thermaldecomposition to the sag controlling temperature, time-varying changesin temperature at the ends of the film and in the middle portion of thefilm are also measured at 30° C. intervals (at the points of time, 500°C., 530° C., 560° C., and 580° C., in a case where the startingtemperature of thermal decomposition in the widthwise middle portion ofthe film and the sag controlling temperature are 500° C. and 580° C.,respectively) starting from the starting temperature of the widthwisemiddle portion of the film. Such measurement is performed to confirmthat at least one of the four measured temperatures, preferably allthese four measured temperatures, satisfy such a condition that thetemperature gradient over an area extending from the both ends to themiddle portion is not less than 2.5° C./m.

The following will describe widthwise temperature control of a polymerfilm in a case where the sag controlling step is performed in thecontinuous processing method. As shown in FIG. 8, a polymer film ispassed through a heat treatment apparatus which has been set so that atemperature gradient is given to the film in a lengthwise direction ofthe film (in this case, corresponding to the MD direction as well)within a temperature range from the starting temperature of thermaldecomposition to the sag controlling temperature. As a result, thepolymer film receives a thermal hysteresis within the temperature rangefrom the starting temperature of thermal decomposition to the sagcontrolling temperature. In this case, the sag controlling step can beperformed by subjecting a polymer film passing through the above heattreatment apparatus to heat treatment with a temperature differencegiven between the widthwise ends of the polymer film and the widthwisemiddle portion of the polymer film.

In the temperature range from the starting temperature of thermaldecomposition to the sag controlling temperature, temperatures at theends of the film and in the middle portion of the film are measured, bymeans of 0.5 mm-diameter sheathed type K thermocouples placed in contactwith the both ends of the film and the middle portion of the film, at30° C. intervals (see FIG. 8; at the points of time, 500° C., 530° C.,560° C., and 580° C., in a case where the starting temperature ofthermal decomposition in the widthwise middle portion of the film andthe sag controlling temperature are 500° C. and 580° C., respectively)starting from the starting temperature of the widthwise middle portionof the film. Such measurement is performed to confirm that at least oneof the four measured temperatures, more preferably all these fourmeasured temperatures, satisfy such a condition that the temperaturegradient over an area extending from the both ends to the middle portionis not less than 2.5° C./m.

The temperature range from the starting temperature of thermaldecomposition of the polymer film to the sag controlling temperatureneeds to satisfy a condition such that the temperatures of the polymerfilm at the both widthwise ends are set higher than the temperature ofthe polymer film in the widthwise middle portion and a condition suchthat a temperature gradient over an area extending from the bothwidthwise ends to the widthwise middle portion of the polymer film isnot less than 2.5° C./m. Particularly, it is preferable that, at the sagcontrolling temperature, temperature measurement points in the sagcontrolling step satisfy such a condition that the temperature gradientover an area extending from the both widthwise ends of the polymer filmto the widthwise middle portion of the polymer film is not less than2.5° C./m. Further, it is more preferable that at least 70% of thetemperature measurement points in the sag controlling step satisfy sucha condition that the temperature gradient over an area extending fromthe both widthwise ends of the polymer film to the widthwise middleportion of the polymer film is not less than 2.5° C./m. Although it isparticularly preferable that the difference in temperature constantlyfall within a certain range, the difference in temperature may varywithin a range yielding the effect of the first embodiment of thepresent invention.

In terms of productivity, the sag controlling step according to thefirst embodiment of the present invention is preferably performed by thecontinuous long film processing method. Also, from the viewpoint offacilitating widthwise temperature control of the polymer film, the sagcontrolling step according to the first embodiment of the presentinvention is preferably performed by the continuous long film processingmethod.

Examples of a method of giving a difference in temperature between thewidthwise ends of the polymer film and the middle portion of the polymerfilm include: a method of controlling the temperatures of the widthwiseends of the polymer film and the temperature of the middle portion ofthe polymer film by independently controlling separate heaters which arerespectively placed close to the side of the widthwise ends of thepolymer film and the side of the middle portion of the polymer film; anda method of giving a desired difference in temperature with use of aheat insulator or the like. These methods are not the onlypossibilities, and any method may be employed.

<Graphite Film>

The graphite film can be produced by heat-treating a polymer filmserving as a raw material film. The polymer film suitable for productionof a graphite film is exemplified by a polymer film made of at least onetype of resin selected from the group consisting of polyimide,polyamide, polyoxadiazole, polybenzothiazole, polybenzobisazole,polybenzooxazole, polybenzobisoxazole, polyparaphenylenevinylene,polybenzoimidazole, polybenzobisimidazole, and polythiazole.

Among those named above, the polyimide film is an especially favorablepolymer film, because the polyimide film is more likely to develop alayer structure of graphite through carbonization and graphitizationthan any other polymer film that is made from an organic material.

Note that the term “polymer film” of the present invention encompasses aheat-treated film obtained by treating a polymer film with heat.Further, the term “heat-treated film” means a film that is obtained as aresult of heat treatment to a polymer film and shows weight loss ofabove 0% and not more than 40%. Note that a film obtained as a result ofheat treatment to the polymer film or the heat-treated film and showingweight loss of more than 40% is defined as a “carbonized film”. Further,a film obtained by heat-treating any film selected from the followingfilms: the polymer film; the heat-treated film; and the carbonized filmat a temperature of 2000° C. or higher is defined as a “graphite film”.

Weight measurement is performed in a manner as described in Examples; afilm is allowed to stand for 24 hours in an environment having atemperature of 23° C. and a humidity of 50%, and a value of the weightof the film is measured in an environment having a temperature of 23° C.and a humidity of 50%.

There is no particular limitation on the thickness of the polymer film.Although a polymer film of a desired thickness can be employed, it ispreferable that the thickness of the polymer film be, for example, inthe range from 50 to 125 μm. There is a tendency that the smaller thethickness of the polymer film, the lesser the depth of the sag and thebetter reproducibility of the sag.

Further, there is no particular limitation on the width of the polymerfilm. However, it is preferable that a polymer film having a width, forexample, in the range from 50 to 300 mm be employed. There is a tendencythat the smaller the width of the polymer film, the smaller the sag.

Further, the carbonization step for the polymer film is not essential.As indicated in Examples described later, even in a case where thecarbonization step is not carried out, the sag control technique of thepresent invention can be utilized without any problem.

<Method for Producing Graphite Film>

Examples of a method for producing a graphite film from a polymer filmencompass a method undergoing a carbonization step, a graphitizationstep, and a pressurizing step, to obtain a graphite film. In such amethod, for example, in the carbonization step, a polymer film servingas a starting material is carbonized by heat-treating the polymer filmeither under reduced pressure or in an inert gas. In the carbonizationstep, heat treatment is performed usually at a temperature ofapproximately 1000° C. For example, in the case of preliminary heattreatment performed at a heating rate of 10° C. per minute from roomtemperature, it is desirable that heat treatment be performed with thetemperature kept in a temperature range of 1000° C. for approximately 30minutes. At the stage of the preliminary heat treatment, pressure may beapplied to the polymer film in a direction parallel to a surface of thefilm so that the film does not lose its orientation.

For example, the graphitization step, which follows the carbonizationstep, is performed with the carbonized film set in anultrahigh-temperature furnace. The graphitization step is performedeither under a reduced pressure or in an inert gas. It is mostappropriate to use argon as the inert gas, and it is more preferablethat a small amount of helium be added to argon. In the graphitizationstep, heat treatment is performed preferably at a temperature of 2400°C. or higher, more preferably at a temperature of 2600° C. or higher,even more preferably at a temperature of 2800° C. or higher, orespecially preferably at a temperature of 2900° C. or higher. Note thatthe graphitization step may be performed in succession following thecarbonization step, or may alternatively be performed after coolingafter the carbonization step.

A graphite film obtained through the carbonization step and thegraphitization step is in a foamed state in which the graphite layer hasbeen uplifted by the generation of internal gases such as N₂ and/or afiller (phosphoric acid filler), which does not involve formation of agraphite skeleton. In the case of a graphite film that is in a foamedstate after the graphitization step, the folding endurance can beimproved, for example, by performing the pressurizing step, such ascompression treatment or rolling treatment.

<Environment and Other Conditions Inside Furnace in the Sag ControllingStep>

The sag controlling step of the first embodiment of the presentinvention may be performed in an inert gas (such as nitrogen or argon),an oxygen atmosphere, vacuum, or an atmosphere under a reduced pressure.

<Device for Controlling Tension>

In a case where the sag controlling step is performed through thecontinuous long film producing process of the first embodiment of thepresent invention, the polymer film may be heat-treated with a tensionapplied to the polymer film by using tension adjustment devices somounted, for example, upstream and downstream of the heat treatmentapparatus as to adjust the tension of the polymer film. Such anadjustment device for controlling tension is achieved, for example,through a method of applying torque to a rotating shaft of a wind-offdevice as indicated by reference numeral 81 in FIG. 8.

In the first embodiment of the present invention, in a case where thesag controlling step is carried out through the continuous long filmproducing process, a pulling strength applied to the polymer film is notless than 5 kgf/cm² and not more than 500 kgf/cm², preferably not lessthan 10 kgf/cm² and not more than 300 kgf/cm², or more preferably notless than 20 kgf/cm² and not more than 100 kgf/cm². By performing thesag controlling step with a pulling strength of not less than 5 kgf/cm²,it is possible to reduce the wrinkling of the polymer film which iscaused by shrinkage of the polymer film through thermal composition.Further, by performing the sag controlling step with a pulling strengthof not more than 500 kgf/cm², it is possible to prevent breakage of thepolymer film which may occur due to an excess stress applied to thepolymer film.

<Total Transmittances of Polymer Film and Polymer Film Having beenSubjected to the Sag Controlling Step>

It is preferable that the total transmittances of a polymer film and apolymer film having been subjected to the sag controlling step are lowerthan the total transmittance of a polymer film in an initial stage(which refers to a state in room temperature (23° C., 50% humidity)before the heat treatment is started. A method of measuring the totaltransmittance of the polymer film having been subjected to the sagcontrolling step is described in Examples. The total transmittance ofthe polymer film having been subjected to the sag controlling step ispreferably not more than 10.0, more preferably not more than 6.0, oreven more preferably not more than 1.0.

<Load to be Applied to Polymer Film in its Thickness Direction>

In the first embodiment of the present invention, in a case where thesag controlling step is carried out through the continuous long filmproducing process, it is preferable that a load be applied to thepolymer film in its thickness direction in the heat treatment apparatus.An example of a method for applying a load encompasses, but is notparticularly limited to, a method in which as shown in FIG. 8, a polymerfilm moves along a hearth with a weight placed on the polymer film. Alower limit to the load that is applied to the polymer film in itsthickness direction is preferably not less than 0.1 g/cm², morepreferably not less than 0.5 g/cm², or even more preferably not lessthan 1 g/cm². An upper limit to the load applied to the polymer film inits thickness direction is preferably not more than 50 g/cm², morepreferably not more than 20 g/cm², or even more preferably not more than10 g/cm². With a load of not less than 0.1 g/cm², it is possible toreduce the wrinkling of the polymer film due to shrinkage of the polymerfilm through thermal decomposition. Further, with a load of not morethan 50 g/cm², the polymer film can be prevented from breaking underexcess tension.

<Line Speed>

In the first embodiment of the present invention, in a case where thesag controlling step is carried out through the continuous long filmproducing process, a line speed for the polymer film (hereinafter, alsoreferred to as “line speed”) means the speed at which the film isconveyed in the sag controlling step. The line speed is not less than 10cm/min and not more than 500 cm/min, preferably not less than 20 cm/minand not more than 300 cm/min, or more preferably not less than 30 cm/minand not more than 150 cm/min. In terms of productivity, the line speedis preferably not less than 10 cm/min. Further, with a line speed of notmore than 500 cm/min, it is possible to perform control of a temperaturedistribution in the heat treatment apparatus, thus enabling control ofsag.

<Birefringence>

The term “birefringence” means a difference between (i) a refractiveindex of the film in any direction in a plane of the film and (ii) arefractive index of the film in its thickness direction. In the firstembodiment of the present invention, there is no particular limitationon the birefringence of the polymer film. It is safe that a polymer filmas employed has a birefringence of preferably not less than 0.08, morepreferably not less than 0.10, even more preferably 0.12, or especiallypreferably not less than 0.14. Carbonization and graphitization of thepolymer film having a birefringence of not less than 0.08 progress moreeasily, with the result that a graphite film having a graphite layerdeveloped is more likely to be produced.

<Sag Controlling Step in Two or More Separate Stages>

The sag controlling step according to the first embodiment of thepresent invention may be performed in two or more separate stages. Forexample, assume that the sag controlling step is performed under thecondition that the starting temperature of thermal decomposition is 500°C. and the sag controlling temperature is 655° C. In this case, the sagcontrolling step may be continuously performed in the temperature rangefrom 500° C. to 655° C., in a constant temperature gradient set andmaintained such that the temperatures of the widthwise ends of the filmare higher than the temperature of the widthwise middle portion of thefilm. However, the sag controlling step may be performed in analternative manner. That is, a first heat treatment is performed in atemperature range from 500° C. to 540° C., and a second heat treatmentis performed in a temperature range from 540° C. to 655° C.(hereinafter, such a sag controlling step is referred to as “a separatesag controlling step”.). In a case where the separate sag controllingstep is performed, a temperature gradient such that the temperatures ofthe widthwise ends of the film are higher than the temperature of thewidthwise middle portion of the film in a first sag controlling step maybe varied from the temperature gradient in a second or subsequent sagcontrolling step, instead of being identical to the temperature gradientin the second or subsequent sag controlling step. In this case, it ispossible to obtain a combined effect of the effect achieved by the firstsag controlling step performed in the range from 500° C. to 540° C. andthe effect achieved by the second sag controlling step performed in therange from 540° C. to 655° C.

<Difference in Lengthwise Length Between Widthwise Ends and WidthwiseMiddle Portion of Graphite Film>

A difference in lengthwise length between the widthwise ends andwidthwise middle portion of a graphite film can be evaluated from aresult of the measurement of lengths of graphite film strips into whicha graphite film has been slit. More specifically, a graphite film is cutto be 500 mm in lengthwise length. In cutting the graphite film, a cutside of the graphite film should be vertical to the length 33 of themiddle portion of the graphite film, as shown in FIG. 3. Further, thelength of 500 mm is based on the measurement of the length 33 of themiddle portion of the graphite film. Next, the middle portion 33 and theends 34 and 36 of the graphite film are slit into 10 mm-wide strips.Subsequently, the lengths of the strips are measured, and a differencein length is then calculated from the lengths thus measured.

(2. Second Embodiment of the Present Invention)

The “sag” of a graphite film is the same as that in the firstembodiment, and as such, is omitted here.

The second embodiment of the present invention relates to a graphitefilm with controlled sag and a production method for producing agraphite film with controlled sag. In the second embodiment of thepresent invention, the inventors of the present invention found that inorder to obtain a sag of a graphite film, it is important to treat apolymer film with heat while controlling the temperatures of the polymerfilm at both widthwise ends and the temperature of the polymer film in awidthwise middle portion within the temperature range from a startingtemperature of thermal decomposition of the polymer film to a sagcontrolling temperature of the polymer film (hereinafter, such a heattreatment step is referred to as “sag controlling step”). That is, agraphite film of the second embodiment of the present invention isobtained by subjecting a polymer film to the sag controlling step andthen treating the film obtained in the sag controlling step with heat ata temperature of 2000° C. or higher. The second embodiment of thepresent invention is an embodiment to obtain a graphite film withcontrolled sag, by subjecting the polymer film to a special heattreatment at a temperature in a particular temperature range in an earlystage of decomposition of the polymer film.

A graphite film obtained by a graphite film production method includingthe sag controlling step according to the second embodiment of thepresent invention has a shape controlled along the widthwise directionof the film. The film having such a controlled shape is classifiedinto: 1) a graphite film having a sag in a middle portion thereof; 2) aflat graphite film having no sag; and 3) a graphite film having a sag atone end thereof.

The graphite films 1) through 3) each having a shape controlled alongthe widthwise direction of the film can be obtained by the followingproduction methods.

1) Method for producing a graphite film having a sag in the middleportion thereof.

The inventors of the present invention found that a graphite film havinga sag in the middle portion thereof is obtained by using a method forproducing a graphite film including: a sag controlling step of treatinga polymer film with heat so that the temperatures of the polymer film atboth widthwise ends are lower than the temperature of the polymer filmin a widthwise middle portion within a temperature range from a startingtemperature of thermal decomposition of the polymer film to a sagcontrolling temperature of the polymer film and so that a temperaturegradient over an area extending from the both widthwise ends of thepolymer film toward the widthwise middle portion of the polymer film isnot more than −2.5° C./m; and a step of treating the film obtained inthe sag controlling step with heat at a temperature of 2000° C. orhigher after the sag controlling step.

According to the second embodiment of the present invention, in order toobtain a graphite film having a sag in the widthwise middle portionthereof, a temperature gradient over an area extending from the bothwidthwise ends to the widthwise middle portion is not more than −2.5°C./m, preferably not more than −5° C./m, or more preferably not morethan 10° C./m. Although being not particularly limited, an upper limitto the temperature gradient over an area extending from the bothwidthwise ends to the widthwise middle portion is preferably not lessthan −100° C./m, more preferably not less than −50° C./m, or even morepreferably not less than −25° C./m. It is preferable that each of thetemperature gradients over an area extending from one of the bothwidthwise ends to the widthwise middle portion and over an areaextending from the other of the both widthwise ends to the widthwisemiddle portion is not more than −2.5° C./m, because it realizes agraphite film sufficiently sagging in the middle portion thereof.Further, it is preferable that each of the temperature gradients over anarea extending from one of the both ends to the middle portion and overan area extending from the other of the both widthwise ends to thewidthwise middle portion is not less than −100° C., because it realizesa graphite film hardly torn when a tension is applied to the graphitefilm along the lengthwise direction thereof.

Through this production method, a graphite film 41 having a sag in awidthwise middle portion thereof (for example, see FIG. 4) is obtained.

(Sag b-value of Graphite Film in Middle Portion)

The degree of sag of a graphite film having a sag in a middle portionthereof can be evaluated from a result of the measurement of a sagb-value. The sag b-value refers to a sag that occurs in a widthwisemiddle portion of a graphite film, when the film is set in a similarstate to that in the measurement of sag described in JIS C2151.

The b-value of the graphite film having a sag in the middle portionthereof, as obtained in the second embodiment of the present invention,is not less than 5 mm, preferably not less than 20 mm, and morepreferably not less than 40 mm. Although being not particularly limited,an upper limit to the b-value is preferably not more than 120 mm, morepreferably not more than 100 mm, or even more preferably not more than80 mm. A graphite film having the b-value of not less than 5 mm ispreferable because the graphite film is less likely to suffer fromfolding wrinkles at ends thereof when subjected to the rolling process.Meanwhile, a graphite film having the b-value of not more than 120 mm ispreferable because the graphite film is less likely to be torn whenstretched in the lengthwise direction thereof. A method for measuringthe b-value will be described in detail in the section “Examples”.

2) Method for Producing Flat Graphite Film Having No Sag

The inventors of the present invention found that a flat graphite filmhaving no sag is obtained by using a method for producing a graphitefilm including: a sag controlling step of treating a polymer film withheat within a temperature range from a starting temperature of thermaldecomposition of the polymer film to a sag controlling temperature ofthe polymer film so that a temperature gradient over an area extendingfrom both widthwise ends of the polymer film toward a widthwise middleportion of the polymer film is not less than −2.4° C./m and not morethan 2.4° C./m; and a step of treating the film obtained in the sagcontrolling step with heat at a temperature of 2000° C. or higher afterthe sag controlling step.

According to the second embodiment of the present invention, in order toobtain a flat graphite film that has no sag, it is preferable that thetemperature gradient over an area extending from the both ends towardthe middle portion be not less than −2.4° C./m and not more than 2.4°C./m, preferably not less than −2.0° C./m and not more than 2.0° C./m,or more preferably not less than −1.0° C./m and not more than 1.0° C./m.In order to obtain a flat graphite film having a small sag, it ispreferable that each of the temperature gradients over an area extendingfrom one of the both ends toward the middle portion and over an areaextending from the other of the both ends toward the middle portion benot less than be −2.4° C./m and not more than 2.4° C./m.

Through this production method, a graphite film 42 that is flat and hasno sag (for example, see FIG. 4) is obtained.

(Sag Described in JIS C2151)

The flatness of a graphite film that is flat and has no sag can beevaluated by measuring a sag described in JIS C2151.

In the second embodiment of the present invention, it is preferable thatthe sag of a graphite film that is flat and has no sag be not more than4.9 mm, preferably not more than 4 mm, more preferably not more than 3mm, even more preferably not more than 1 mm, or especially preferably0.1 mm. There is no particular lower limit. In order for the resultinggraphite film to be able to laminated to a copper foil tape withoutwrinkles, it is preferable that the sag be not more than 4.9 mm. Amethod for measuring a sag will be described in detail in the section“Examples”.

3) Method for Producing Graphite Film Having sag at One End.

The inventors of the present invention found that a graphite film thatis flat with sag at one end thereof is obtained by using a method forproducing a graphite film including: a sag controlling step of treatinga polymer film with heat within a temperature range from a startingtemperature of thermal decomposition of the polymer film to a sagcontrolling temperature of the polymer film so that TemperatureA≥Temperature B≥Temperature C and Temperature A≠Temperature C (whereTemperature A is the temperature of one widthwise end of the polymerfilm, Temperature B is the temperature of a widthwise middle portion ofthe polymer film, and Temperature C is the temperature of the otherwidthwise end of the polymer film) and so that a temperature gradientfrom Temperature A to Temperature C is not less than 2.5° C./m; and astep of treating the film obtained in the sag controlling step with heatat a temperature of 2000° C. or higher after the sag controlling step.

In the second embodiment of the present invention, it is preferable, forthe purpose of obtaining a graphite film 46 with sag at one end, thatthe temperature gradient from Temperature A to Temperature C be not lessthan 2.5° C./m, preferably 5° C./m, or more preferably 10° C./m. It ispreferable, for the purpose of obtaining a graphite film with sag at oneend, that the temperature gradient from Temperature A to Temperature Cbe not less than 2.5° C./m.

Through this production method, a graphite film 46 with sag at one end(for example, see FIG. 4) is obtained.

(Camber Described in JIS C2151)

The degree of distortion of a graphite film with sag at one end can beevaluated by measuring camber described in JIS C2151.

In the second embodiment of the present invention, it is preferable thatthe camber of a graphite film with sag at one end be not less than 11mm, preferably not less than 15 mm, or more preferably not less than 20mm. Although there is no particular upper limit, it is preferable thatsuch an upper limit be not more than 80 mm, more preferably not morethan 70 mm, or even more preferably not more than 60 mm. With a camberof not less than 11 mm, the graphite film can be easily laminated to acurved plate. Meanwhile, with a camber of not more than 80 mm, in orderfor the resulting graphite film to be hardly torn when stretchedlengthwise, it is preferable that the camber be not more than 80 mm. Amethod for measuring camber will be described in the section “Examples”.

Further, a graphite film sagging in one half area thereof extending froma widthwise middle portion to either one end thereof can be obtained byexecuting a sag controlling step that involves heat treatment under thecondition Temperature A=Temperature B≥Temperature C or under thecondition Temperature A≥Temperature B=Temperature C.

4) Application of the Production Methods in the Second embodiment of thePresent Invention.

Utilization of the concepts in the second embodiment of the presentinvention makes it possible to obtain a graphite film 43 with sags atboth widthwise ends and to, by combining these sags, obtain graphitefilms with various types of sags such as those in the shapes of theletters M and W.

For example, a graphite film 43 with sags at both widthwise ends isobtained by using a method for producing a graphite film including: asag controlling step of treating a polymer film with heat within atemperature range from a starting temperature of thermal decompositionof the polymer film to a sag controlling temperature of the polymer filmso that a temperature gradient over an area extending from bothwidthwise ends of the polymer film toward a widthwise middle portion ofthe polymer film is not less than 2.5° C./m; and a step of treating thefilm obtained in the sag controlling step with heat at a temperature of2000° C. or higher after the sag controlling step.

For example, a graphite film with a sag in the shape of the letter M isobtained by using a method for producing a graphite film including: asag controlling step of treating a polymer film with heat within atemperature range from a starting temperature of thermal decompositionof the polymer film to a sag controlling temperature of the polymer filmso that both widthwise ends of the polymer film and a widthwise middleportion of the polymer film are higher in temperature than the otherportions of the polymer film; and a step of treating the film obtainedin the sag controlling step with heat at a temperature of 2000° C. orhigher after the sag controlling step.

For example, a graphite film with sags in the shape of the letter W isobtained by using a method for producing a graphite film including: asag controlling step of treating a polymer film with heat within atemperature range from a starting temperature of thermal decompositionof the polymer film to a sag controlling temperature of the polymer filmso that both widthwise ends of the polymer film and a widthwise middleportion of the polymer film are lower in temperature than the otherportions of the polymer film; and a step of treating the film obtainedin the sag controlling step with heat at a temperature of 2000° C. orhigher after the sag controlling step.

(Mechanism by which the Effect of the Sag Controlling Step is Developed)

The mechanism by which the effect of the sag controlling step isdeveloped is described below by taking, as an example, the case of agraphite film with sag in a middle portion thereof.

First, in the early stage of thermal decomposition of a polymer film,the polymer film is treated with heat so that both widthwise ends of thepolymer film are relatively lower in temperature than a widthwise middleportion of the polymer film. The polymer film thus given a thermalhysteresis which varies across the width varies across the width inprogress of graphitization in the graphitization step that follows thecarbonization step (i.e. varies in degree of orientation of graphitecrystallites), so that the lengthwise length of the graphite film in themiddle portion is greater than the lengthwise lengths of the graphitefilm at both ends. Thus, when such a graphite film is observed in thewidthwise direction thereof, the appearance of sags of the graphite filmis confirmed in the middle portion of the graphite film, wherein thelengthwise length of the graphite film in the middle portion is longerthan the length of the graphite film at its peripheral portions.

(Relationship Between the Sag Controlling Step and Conventional Methodfor Producing GS)

A usual example of a method for producing a graphite film from a polymerfilm in general is a method including: the carbonization step oftreating the polymer film with heat at a temperature of up toapproximately 1000° C. and the graphitization step of treating acarbonized film thus obtained in the carbonization step at a temperatureof 2600° C. or higher. The sag controlling step according to the presentinvention serves to control a widthwise temperature distribution of thepolymer film in the temperature range in the comparatively-early stageof the carbonization step.

Example of a method for producing a graphite film that involves theexecution of the sag controlling step according to the second embodimentof the present invention encompass: a method of performing the sagcontrolling step and a temperature decreasing step in succession andthen performing the carbonization step and the graphitization step; anda method of performing both the sag controlling step and thecarbonization step in one process (performing the sag controlling stepand subsequently performing the carbonization step, without atemperature decrease intervening between the sag controlling step andthe carbonization step) and then performing the graphitization step.

<Definitions of Ends and Middle Portions of Polymer Film and of GraphiteFilm>

Omitted here as they are the same as those in the first embodiment.

<Widthwise Temperature Gradient in the Sag Controlling Step)

A graphite film with controlled sag is obtained by (a) treating apolymer film with heat while controlling the temperatures of the polymerfilm at both widthwise ends of the polymer film and the temperature ofthe polymer film in a widthwise middle portion of the polymer filmwithin a temperature range from a starting temperature of thermaldecomposition of the polymer film to a sag controlling temperature ofthe polymer film and then (b) executing the graphitization step. In thisregard, a graphite film with controlled sag can also be obtained byarbitrarily setting the widthwise temperature gradient and/ortemperature distribution of the film in a temperature range over the sagcontrolling temperature.

Further, in the second embodiment of the present invention, thetemperature gradient over an area extending from both ends toward amiddle portion refers to a temperature gradient over an area extendingfrom an end 1 toward the middle portion and a temperature gradient overan area extending from an end 2 (i.e. the other end that is differentfrom the end 1) toward the middle portion. With use of the temperaturesof a film at the both ends and in the middle portion on a given straightline perpendicular to the lengthwise direction of the film and the widthof the film as shown in FIG. 5, the temperature gradient over an areaextending from the both ends toward the middle portion is expressed bythe following equation:Temperature Gradient over Area Extending from Both Ends toward MiddlePortion=(Temperature of Film at Both Ends−Temperature of Film in MiddlePortion)/(Width of Film/2)×100.

The temperatures of the film at the both ends and in the middle portionacross a given width are values measured at the same time. In thepresent invention, Temperature A, Temperature B, and Temperature C referto those temperatures measured at the points 53, 54, and 55 shown inFIG. 5 or those temperatures measured at the points 55, 54, and 53 shownin FIG. 5, respectively. Further, in the present invention, thetemperature gradient from Temperature A to Temperature C is expressed bythe following equation:Temperature Gradient from Temperature A to Temperature C=(TemperatureA−Temperature C/(Width of Film/2)×100.

Temperatures A and C at a given width are values measured at the sametime.

<Decomposition Reaction and Weight Loss Rate in the Sag ControllingStep>

Omitted here as they are the same as those in the first embodiment.

<Method for Measuring the Temperature of a Film>

The second embodiment of the present invention makes it possible tocontrol sag by treating a polymer film with heat while controlling thetemperature of the polymer film widthwise within a temperature range ofa starting temperature of thermal decomposition of the polymer film to asag controlling temperature of the polymer film. Specifically, themethod for measuring the temperature of a film in the second embodimentis the same as that in the first embodiment, and as such, is omittedhere.

<Starting Temperature of Thermal Decomposition of the Polymer Film andthe Sag Controlling Temperature of the Polymer Film>

The starting temperature of thermal decomposition of a polymer film inthe second embodiment of the present invention is the same as that inthe first embodiment.

The sag controlling temperature of a polymer film in the secondembodiment of the present invention, too, is the same as that in thefirst embodiment. In a case where the sag controlling temperature is atemperature at which a weight loss rate of a polymer film does notexceed 20.0% (upper limit value to the sag control), the sag controllingstep may be a single-stage sag controlling step or a multi-stage sagcontrolling step. Alternatively, the sag controlling step may beperformed two or more times. By all these sag controlling steps, sagamplification can be realized. In such a case, the temperatures ofwidthwise ends of a film are set at the desired temperature until thesag controlling temperature reaches a temperature at which the weightloss rate of the film exceeds 20%. In a temperature range in which aweight loss rate exceeds 20.0%, there is no difference between a sag ofa graphite film obtained as a final product under the condition that thetemperatures of widthwise ends of a film are set at the desiredtemperature and a sag of a graphite film obtained as a final productwithout such a condition.

A specific measurement of a temperature at which a polymer film shows aweight loss rate of 20%, as the most preferable sag controllingtemperature according to the second embodiment of the present invention,too, is the same as that in the first embodiment, and as such, is notdescribed here.

<Starting Temperature of Thermal Decomposition of Polymer Film as Usedin Examples of Second embodiment of the Present Invention and SagControlling Temperature of the Polymer Film>

For polyimide films as used in Examples of the second embodiment of thepresent invention (polyimide films manufactured by Kaneka Corporation:Apical AH of 75 μm in thickness; and Apical NPI of 75 μm in thickness),the starting temperature of thermal decomposition of these polyimidefilms and the sag controlling temperature thereof are the same as thosein the first embodiment. In a case where the sag controlling temperaturedoes not exceed 655° C. (upper limit to the sag control), the sagcontrolling step may be a single-stage sag controlling step or amulti-stage sag controlling step. Alternatively, the sag controllingstep may be performed two or more times. By all these sag controllingsteps, sag amplification can be realized. In this case, the temperaturesof widthwise ends of a film are set at the desired temperature until thesag controlling temperature reaches a temperature exceeding 655° C. In atemperature range exceeding 655° C., there is no difference between asag of a graphite film obtained as a final product under the conditionthat the temperatures of widthwise ends of a film are set at the desiredtemperature and a sag of a graphite film obtained as a final productwithout such a condition.

<Method for Performing the Sag Controlling Step>

In the sag controlling step, any method may be employed, withoutparticular limitation, as a method of treating a polymer film with heatin a widthwise temperature gradient given to the polymer film. Oneexample of such a method is a method of holding a sheet-type polymerfilm (which means “one or more polymer films in sheet form”) byinserting the polymer film into a graphite jig within a heat treatmentapparatus, and then heat-treating the polymer film batchwise (sheetbatch method), as shown in FIG. 18. The other example is a method ofholding a polymer film by wrapping around a graphite cylindricalcontainer, and then heating the polymer film batchwise with heat(cylindrical batch method), as shown in FIG. 19. Another example is amethod of subjecting a long polymer film to heat treatment whilecontinuously supplying the long polymer film into the heat treatmentapparatus (continuous processing method or continuous long filmprocessing method), as shown in FIG. 20.

Note that the widthwise direction according to the second embodiment ofthe present invention is a direction along which a difference intemperature is given in the sag controlling step. In a case where a longfilm is to be employed, the widthwise direction thereof, which is notparticularly limited, is preferably a short side of the film (adirection vertical to the lengthwise direction), from a viewpoint ofenabling a further development of the effect of sagging. From a similarviewpoint, in a case where a continuous long film processing method isto be employed, it is preferable that the widthwise direction ispreferably a TD direction rather than a MD direction.

In a case where the sag controlling step is performed in the sheet batchmethod, temperatures of the polymer film are increased within atemperature range from the starting temperature of thermal decompositionof the polymer film to the sag controlling temperature thereof in such astate that widthwise temperature control of a polymer film is carriedout (see one example of widthwise temperature distribution of a polymerfilm shown in FIG. 18). In this case, the temperature range from thestarting temperature of thermal decomposition of the polymer film to thesag controlling temperature needs to be controlled such that adifference in temperature across the width of the polymer film fallswithin the desired range. Particularly, it is preferable that, at thesag controlling temperature, temperature measurement points in the sagcontrolling step satisfy the desired condition for the difference intemperature across the widths of the polymer film. Further, it ispreferable that at least 70% of the temperature measurement points inthe sag controlling step satisfy the desired condition for thedifference in temperature across the widths of the polymer film.Although it is particularly preferable that the difference intemperature constantly fall within a certain range, the difference intemperature may vary within a range yielding the effect of the presentinvention.

The measurement of temperatures of a polymer film is performed, as shownin FIG. 18, by means of 0.5 mm-diameter sheathed type K thermocouplesplaced in contact with the both ends of the polymer film and the middleportion of the polymer film at intervals of 100 mm along the lengthwisedirection of the polymer film.

In the temperature range from the starting temperature of thermaldecomposition to the sag controlling temperature, time-varying changesin temperature at the ends of the film and in the middle portion of thefilm are also measured at 30° C. intervals (at the points of time, 500°C., 530° C., 560° C., and 580° C., in a case where the startingtemperature of thermal decomposition in the widthwise middle portion ofthe film and the sag controlling temperature are 500° C. and 580° C.,respectively) starting from the starting temperature of the widthwisemiddle portion of the film. Such measurement is performed to confirmthat for at least one of the four measured temperatures, preferably allthese four measured temperatures, a difference in temperature across thewidth of the polymer film satisfies the desired condition.

As in the case where the sag controlling step is performed in the sheetbatch method, in a case where the sag controlling step is performed inthe cylindrical batch method, widthwise temperature control of a polymerfilm is carried out by increasing temperatures of the polymer filmwithin a temperature range from the starting temperature of thermaldecomposition of the polymer film to the sag controlling temperaturethereof in such a state that a difference in temperature is givenbetween the widthwise ends of the polymer film and the middle portionthereof (see one example of widthwise temperature distribution of apolymer film shown in FIG. 19). In this case, the temperature range fromthe starting temperature of thermal decomposition of the polymer film tothe sag controlling temperature thereof needs to be controlled such thata difference in temperature across the width of the polymer film fallswithin the desired range. Particularly, it is preferable that, at thesag controlling temperature, temperature measurement points in the sagcontrolling step satisfy the desired condition for the difference intemperature across the widths of the polymer film. Further, it ispreferable that at least 70% of the temperature measurement points inthe sag controlling step satisfy the desired condition for thedifference in temperature across the widths of the polymer film.Although it is particularly preferable that the difference intemperature constantly fall within a certain range, the difference intemperature may vary within a range yielding the effect of the presentinvention.

The measurement of temperatures of a polymer film is performed, as shownin FIG. 19, by means of 0.5 mm-diameter sheathed type K thermocouplesplaced in contact with the both ends of the polymer film and the middleportion of the polymer film at the respective points circumferentiallyprovided at 90-degree intervals.

In the temperature range from the starting temperature of thermaldecomposition to the sag controlling temperature, time-varying changesin temperature at the ends of the film and in the middle portion of thefilm are also measured at 30° C. intervals (at the points of time, 500°C., 530° C., 560° C., and 580° C., in a case where the startingtemperature of thermal decomposition in the widthwise middle portion ofthe film and the sag controlling temperature are 500° C. and 580° C.,respectively) starting from the starting temperature of the widthwisemiddle portion of the film. Such measurement is performed to confirmthat for at least one of the four measured temperatures, preferably allthese four measured temperatures, a difference in temperature across thewidth of the polymer film satisfies the desired condition.

The following will describe widthwise temperature control of a polymerfilm in a case where the sag controlling step is performed in thecontinuous processing method. As shown in FIG. 20, a polymer film ispassed through a heat treatment apparatus which has been set so that atemperature gradient is given to a film in a lengthwise direction of thefilm (in this case, corresponding to the MD direction as well) within atemperature range from the starting temperature of thermal decompositionto the sag controlling temperature. As a result, the polymer filmreceives a thermal hysteresis within the temperature range from thestarting temperature of thermal decomposition to the sag controllingtemperature. In this case, the sag controlling step can be performed bysubjecting a polymer film passing through the above heat treatmentapparatus to heat treatment with a temperature difference given betweenthe widthwise ends of the polymer film and the widthwise middle portionof the polymer film.

In the temperature range from the starting temperature of thermaldecomposition to the sag controlling temperature, temperatures at theends of the film and in the middle portion of the film are measured, bymeans of 0.5 mm-diameter sheathed type K thermocouples placed in contactwith the both ends of the film and the middle portion of the film, at30° C. intervals (see FIG. 8; at the points of time, 500° C., 530° C.,560° C., and 580° C., in a case where the starting temperature ofthermal decomposition in the widthwise middle portion of the film andthe sag controlling temperature are 500° C. and 580° C., respectively)starting from the starting temperature of the widthwise middle portionof the film. Such measurement is performed to confirm that for at leastone of the four measured temperatures, preferably all these fourmeasured temperatures, a difference in temperature across the width ofthe polymer film satisfies the desired condition.

The temperature range from the starting temperature of thermaldecomposition of the polymer film to the sag controlling temperatureneeds to satisfy the desired condition for a difference in temperatureacross the width of the polymer film. Particularly, it is preferablethat, at the sag controlling temperature, temperature measurement pointsin the sag controlling step satisfy the desired condition for thedifference in temperature across the width of the polymer film. Further,it is more preferable that at least 70% of the temperature measurementpoints in the sag controlling step satisfy the desired condition for thedifference in temperature across the width of the polymer film. Althoughit is particularly preferable that the difference in temperatureconstantly fall within a certain range, the difference in temperaturemay vary within a range yielding the effect of the second embodiment ofthe present invention.

In terms of productivity, the sag controlling step according to thesecond embodiment of the present invention is preferably performed bythe continuous long film processing method. Also, from the viewpoint offacilitating widthwise temperature control of the polymer film, the sagcontrolling step according to the first embodiment of the presentinvention is preferably performed by the continuous long film processingmethod.

Examples of a method of controlling the temperature of the polymer filmwidthwise include: a method of controlling the temperatures of thewidthwise ends of the polymer film and the temperature of the middleportion of the polymer film by independently controlling separateheaters which are respectively placed close to the side of the widthwiseends of the polymer film and the side of the middle portion of thepolymer film; and a method of giving a desired difference in temperaturewith use of a heat insulator or the like. These methods are not the onlypossibilities, and any method may be employed.

<Graphite Film>

The graphite film in the second embodiment of the present invention isthe same as that in the first embodiment.

<Method for Producing Graphite Film>

The method for producing a graphite film, too, is the same as that inthe first embodiment.

<Environment and Other Conditions inside Furnace in the Sag ControllingStep>

The sag controlling step of the second embodiment of the presentinvention may be performed in an inert gas (such as nitrogen or argon),an oxygen atmosphere, vacuum, or an atmosphere under a reduced pressure.

(Device for Controlling Tension>

In the second embodiment of the present invention, too, the tensionadjustment device can be utilized in the same way as in the firstembodiment.

<Total Transmittances of a Polymer Film and of Polymer Film Having beenSubjected to the Sag Controlling Step>

The total transmittances of a polymer film and of a polymer film havingbeen subjected to the sag controlling step are the same as those in thefirst embodiment.

<Load to be Applied to Polymer Film in its Thickness Direction>

A load to be applied to a polymer film in a thickness direction in thesecond embodiment of the present invention, too, is the same as that inthe first embodiment.

<Line Speed>

The line speed in the second embodiment of the present invention, too,is the same as that in the first embodiment.

<Birefringence>

The birefringence in the second embodiment of the present invention,too, is the same as that in the first embodiment.

<Sag Controlling Step in Two or More Separate Stages>

The sag controlling step according to the second embodiment of thepresent invention may be performed in two or more separate stages. Forexample, assume that the sag controlling step is performed under thecondition that the starting temperature of thermal decomposition is 500°C. and the sag controlling temperature is 655° C. In this case, the sagcontrolling step may be continuously performed in the temperature rangefrom 500° C. to 655° C. such that the temperature of the film across thewidth is controlled. However, the sag controlling step may be performedin an alternative manner. That is, a first heat treatment is performedin a temperature range from 500° C. to 540° C., and a second heattreatment is performed in a temperature range from 540° C. to 655° C.(hereinafter, such a sag controlling step is referred to as “a separatesag controlling step”.). In a case where the separate sag controllingstep is performed, widthwise temperature control of the film in a firstsag controlling step may be varied from widthwise temperature control ofthe film in a second or subsequent sag controlling step, instead ofbeing identical to widthwise temperature control of the film in thesecond or subsequent sag controlling step. In this case, it is possibleto obtain a combined effect of the effect achieved by the first sagcontrolling step performed in the range from 500° C. to 540° C. and theeffect achieved by the second sag controlling step performed in therange from 540° C. to 655° C.

<Difference in Lengthwise Length Between Widthwise Ends and WidthwiseMiddle Portion of Graphite Film>

A difference in lengthwise length between the widthwise ends andwidthwise middle portion of a graphite film in the second embodiment ofthe present invention is the same as that in the first embodiment.

(3. Third embodiment of the Present Invention)

A third embodiment of the present invention relates to a graphite filmwith sag of 20.0 mm or less as evaluated according to the filmwindability evaluation under JIS C2151.

Further, the third embodiment of the present invention relates to amethod for producing a graphite film including a straightening processstep of heating treating a raw graphite film with heat up to not lowerthan 2000° C. while applying pressure to the raw graphite film, thestraightening process step including treating the raw graphite film withheat with the raw graphite film wound around an inner core whosediameter accuracy is less than 0.0426%. By straightening the rawgraphite film by using an inner core with high diameter accuracy, a flatgraphite film with sag in a very small amount can be obtained.

The “sag” of a graphite film is the same as that in the firstembodiment, and as such, is omitted here.

The sag of a graphite film in the third embodiment of the presentinvention is not more than 20 mm, preferably not more than 10 mm, morepreferably not more than 5 mm, preferably not more than 4 mm, morepreferably not more than 3 mm, even more preferably not more than 1 mm,or especially preferably not more than 0.1 mm. In order for the graphitefilm to be able to be laminated to a material, such as a copper foiltape, to which it has conventionally been difficult for a graphite filmto be laminated, it is preferable that the sag be not more than 20 mm.

An example of the method for producing a graphite film in the thirdembodiment of the present invention is a method that involves theexecution of a straightening-for-flatness step of treating the rawgraphite film with heat up to not lower than 2000° C. while applyingpressure to the raw graphite film. By using thisstraightening-for-flatness step to control the sagging of the rawgraphite film, a graphite film with improved flatness can be produced.

<Raw Graphite Film>

The thermal diffusivity of the raw graphite film in the third embodimentof the present invention is preferably not less than 0.15 cm² persecond, more preferably not less than 2.0 cm² per second, even morepreferably not less than 4.0 cm² per second, or especially preferablynot less than 7.0 cm² per second.

With a thermal diffusivity of not less than 0.15 cm² per second, thereis only a small change in dimensions during the heat treatmentsufficient progress of the graphitization, so that the straighteningprocess can be easily executed. In particular, in a case where thestraightening process is carried by utilizing a difference in thermalexpansion between the inner core and the raw graphite film wound aroundthe inner core, a small change in dimensions of the raw graphite filmmakes it easy for the raw graphite film to be pushed wide, so that thestraightening effect is easily brought about. Since the raw graphitefilm has been turned into a film that is high in strength, flexible, andhard to tear, rewinding work, which will be described later, is easilycarried out. Furthermore, with a thermal diffusivity of not less than0.15 cm² per second, the raw graphite film is thermally migrates sosmoothly that the straightening process can be uniformly carried out.

A method for measuring the thermal diffusivities of a raw graphite filmand of a graphite film is described in section “Examples”.

Further, in the third embodiment of the present invention, the number oftimes a raw graphite film is bent under MIT folding endurance test ispreferably not less than 100 times, more preferably not less than 500times, even more preferably not less than 5000 times, or especiallypreferably not less than 10000 times.

If the number of times the raw graphite film is folded is not less than100 times, the resulting film will be high in strength, flexible, andhard to tear, so that the rewinding work, which will be described later,is easily carried out.

A method for evaluating a raw graphite film and a graphite film underMIT folding endurance test is described in the section “Examples”.

The straightening process may be performed on a raw graphite film whoseshape needs to be changed, or the straightening process step may beadded to a process for producing a graphite film. Alternatively, agraphite film once subjected to the straightening process may besubjected again to the straightening process as a raw graphite film.

Further, in the third embodiment of the present invention, a rawgraphite film obtained by treating a polymer film with heat at atemperature of 2000° C. or higher is cooled down at least once to atemperature condition of lower than 2000° C., and then the straighteningprocess step is carried out, so that a graphite film straightened forflatness can be obtained. Going through a temperature condition of lowerthan 2000° C. means that a raw graphite film synthesized by heattreatment is cooled down once, which makes it easy to make preparationsfor the straightening process such as the rewinding step.

<Length and Width of Raw Graphite Film>

The width of a raw graphite film means the length of a shorter side of acontinuous sheet of raw graphite film. The width of a raw graphite filmin the third embodiment of the present invention is not particularlylimited. However, with a greater width, the effect of sag control by thestraightening process step can be remarkably exhibited, as a greaterwidth makes it more difficult to control sag. The width of a rawgraphite film in the third embodiment of the present invention ispreferably not less than 100 mm, more preferably not less than 200 mm,or even more preferably not less than 400 mm. With a width of not lessthan 100 mm, the effect of sag control in the third embodiment of thepresent invention can be remarkably exhibited.

The length of a raw graphite film means the length of a longer side of acontinuous sheet of raw graphite film. The length of a raw graphite filmin the third embodiment of the present invention is not particularlylimited. However, it is preferable to have a continuity of not less than4.0 m, more preferably not less than 10.0 m, or even more preferably20.0 m. A continuity of not less than 4.0 m makes it possible to obtaina long graphite film with controlled sag.

<Method for Applying Pressure in the Straightening-for-flatness Step>

In the third embodiment of the invention, the method of straighteningfor flatness is a method in which the flatness of a poorly-flat rawgraphite film with sag is improved by heating the raw graphite film withheat at a temperature of 2000° C. or higher while applying pressure tothe raw graphite film.

Examples of methods for applying pressure include, but are notparticularly limited to, (i) a method in which a load is applied onto asurface of a sheet of raw graphite film, (ii) a method in which a rollof raw graphite film is pushed wide from the inside, and (iii) a methodin which a raw graphite film is stretched.

(i) According to the method in which a load is applied onto a surface ofa sheet of raw graphite film, it is possible, as shown in FIG. 26, toplace a weight on a film surface or to apply pressure by carrying outpressing during heat treatment. According to this method, the pressurerequired for straightening for flatness is not less than 5 g/cm²,preferably not less than 5 g/cm², or more preferably not less than 100g/cm². If the pressure required for straightening for flatness is notless than 5 g/cm², the straightening effect is brought about. An upperlimit on the pressure needs only be such that the film is not damaged.

(ii) An example of the method in which a roll of raw graphite film ispushed wide from the inside is a method in which a raw graphite film iswound around an expandable inner core and pressure is applied from theinner core to the raw graphite film. FIG. 38 shows an example method inwhich a divided inner core pushes a raw graphite film wide outward.

According to this method, the pressure required for straightening forflatness may be 5 g/cm², preferably not less than 5 g/cm², or morepreferably not less than 100 g/cm² from the inner core to the innersurface on the innermost circumference of the raw graphite film woundaround the inner core. With a pressure of not less than 5 g/cm², thestraightening effect is brought about. An upper limit on the pressureneeds only be such that the film is not damaged.

FIG. 27 shows an example method in which a raw graphite film is pushedwide by utilizing a thermal expansion of an inner core. This method ispreferred because the straightening process can be easily carried outwithout providing a special mechanism in a furnace. A raw graphite filmhaving sufficiently progressed in graphitization has its graphitecrystallites highly oriented in the plane direction, and as such, issmall in thermal expansion in the plane direction. When treated withheat while being wound around an inner core made of graphite, the rawgraphite film is easily pushed wide by the inner core having thermallyexpanded with a great effect brought about by the straightening processstep. It is preferable that the raw graphite film be treated while beingwound around the inner core.

According to this method, the pressure required for straightening forflatness cannot be measured, and can instead be defined by the strengthof tight winding in the rewinding step. The strength of tight winding inthe rewinding step in the third embodiment of the present invention isnot less than 1 N·m/m, preferably not less than 5 N·m/m, more preferablynot less than 10 N·m/m, even more preferably not less than 100 N·m/m, orespecially preferably not less than 200 N·m/m. With a strength of tightwinding of not less than 1 N·m/m, sufficient pressure is applied in thestraightening step from the inner core to the inner surface on theinnermost circumference of the raw graphite film wound around the innercore, so that the straightening effect is brought about. An upper limiton the strength of tight winding needs only be such that the film is notdamaged.

(iii) Straightening for flatness can also be carried out by treating araw graphite film with heat while stretching the raw graphite film.

According to this method, the pressure required for straightening forflatness can be defied as tension on the film. The tension required forstraightening for flatness is not less than 5 g/cm, preferably 20 g/cm,or more preferably 50 g/cm. With a tension of not less than 5 g/cm, thestraightening effect is brought about. An upper limit on the tensionneeds only be such that the film is not damaged.

The maximum temperature required for straightening for flatness is notlower than 2000° C., preferably not lower than 2200° C., more preferablynot lower than 2400° C., even more preferably not lower than 2600° C.,still even more preferably not lower than 2750° C., or especiallypreferably not lower than 2800° C. At not lower than 2000° C., a rawgraphite film whose graphite crystallites has begun to rearrangethemselves can be easily straightened. Further, in a case where thestraightening process is carried by utilizing a difference in thermalexpansion between the inner core and the raw graphite film wound aroundthe inner core, a temperature of not lower than 2000° C. widens thedifference in thermal expansion between the inner core and the rawgraphite film, so that the raw graphite film is easily straightened.

Further, the method for producing a graphite film in the thirdembodiment of the present invention may include the straighteningprocess step. The straightening process step is a method forstraightening a raw graphite film for flatness by applying heat andpressure to the raw graphite film, and can be accompanied by rewindingand the like.

A raw graphite film in the third embodiment of the present invention maybe a fired polymer-derived graphite film or a natural graphite film. Afired polymer-derived type of graphite film has its graphitecrystallites better arranged that those of a natural graphite film, andas such, is small in coefficient of thermal expansion in the planedirection. A fired polymer-derived type of graphite film brings about agreater effect when the raw graphite film is straightened while beingwound around the inner core than dose a natural graphite film.

<Example of a Step of Producing a Graphite Film in Which a Carbonizationstep and a Straightening Process Step are Included in a Series ofGraphite Producing Steps>

An example of a step of producing a graphite film in which acarbonization step and a straightening process step are included in aseries of graphite producing steps is described, a) a carbonizationstep, b) graphitization step, and c) a straightening process step may beincluded.

a) The carbonization step is a step of pre-heating a polymer film to atemperature of at least 800° C., and is a step of obtaining a carbonizedfilm through thermolysis of the polymer film. Examples of a method forholding a polymer film include: a method for holding a polymer film bycutting it into a sheet and placing it under a plate or sheet in arectangular jig; a method for holding an elongated polymer film bywinding it around an inner core jig; etc. It is preferable that a jigthat is used for such a method be made of a heat-resistant material suchas a graphite material. Further, it is preferable that the inner corearound which a polymer film is wound be in the shape of a cylinder.Another example of such a method is a method in which a film woundaround a roll is fired while being rewound around another roll.

The resulting carbonized film is a glass-like film that weights about ⅙of the polymer film.

b) The graphitization step is a step of preparing a raw material polymerfilm by heating, at a temperature of not lower than 1800° C., either thecarbonized film prepared in the carbonization step or a polymer film.The maximum graphitization temperature is not lower than 1800° C., morepreferably not lower than 2000° C., more preferably not lower than 2200°C., even more preferably not lower than 2400° C., still even morepreferably not lower than 2600° C., or especially preferably not lowerthan 2800° C. With a temperature of not lower than 1800° C., thegraphitization sufficiently progresses, so that the resulting rawgraphite film is small in change in dimensions and easily improves inflatness in the subsequent straightening process step. Especially in acase where the straightening process is carried out by winding a rawgraphite film around the inner core and utilizing a difference inthermal expansion between the inner core and the raw graphite film, asmall change in dimensions of the raw graphite film makes it easy forthe raw graphite film to be pushed wide by the inner core, so that thestraightening effect is easily brought about. Further, with atemperature of not lower than 1800° C., the resulting graphitized filmis high in strength, flexible, and hard to tear, so that rewinding workis easily carried out.

Either the carbonization step and the graphitization step may be carriedout in a sequential way, or the graphitization step may be carried outalone after the carbonization step is finished. It should be noted thata graphite film finished with the graphitization step but not with thestraightening step is called “raw graphite film”.

c) In a case where the straightening process step is added, it may beperformed on a raw graphite film obtained by carrying out thegraphitization step. Either the straightening process step and thegraphitization step may be carried out in a sequential way, or thestraightening process step may be carried out alone after thegraphitization step is finished.

<Method for Straightening Raw Graphite Film by Treating the Raw GraphiteFilm with Heat with the Raw Graphite Film Wound Around Inner Core andUtilizing Thermal Expansion of the Inner Core>

In the third embodiment of the present invention, the straighteningprocess step is preferably achieved by a method for straightening a rawgraphite film by treating the raw graphite film with heat with the rawgraphite film wound around an inner core. According to this method, inthe course of heat treatment, thermal expansion of the inner core asshown in FIG. 27 causes the raw graphite film, which is low in thermalexpandability, to be pushed wide and straightened. This method makes itpossible to obtain a large-area and highly flat graphite film in alimited space.

(Inner Core)

In the third embodiment of the present invention, the shape of the innercore around which a raw graphite film is wound around may be, but is notparticularly limited to, a cylindrical shape, a polygonal columnarshape, etc. A cylindrical inner core is preferred because it canuniformly transmit power to the raw graphite film in the straighteningprocess so that a good quality graphite film is obtained.

The outer perimeter of the inner core that is used in the thirdembodiment of the present invention is not particularly limited, but ispreferably not less than 62.8000 mm, more preferably 157.0000 mm, oreven more preferably not less than 251.2000 mm. If the inner core has adiameter of 62.8000 mm, the amount of expansion of the inner core is sosufficient that the raw graphite film is pushed wide and straightened.This also allows the graphite film to be less curly and be easilydrawable.

The coefficient of thermal expansion of the inner core that is used inthe third embodiment of the present invention is not particularlylimited, but is preferable not less than 0.3×10⁻⁶/K and not more than7.5×10⁻⁶/K, more preferably not less than 0.7×10⁻⁶/K and not more than6.5×10⁻⁶/K, or even more preferably not less than 2.0×10⁻⁶/K and notmore than 5.0×10⁻⁶/K. If the inner core has a coefficient of thermalexpansion of not less than 0.3×10⁻⁶/K, the amount of expansion of theinner core is so sufficient that the raw graphite film is pushed wideand straightened. Further, if the inner core has a coefficient ofthermal expansion of not more than 7.5×10⁻⁶/K, the raw graphite filmwill not be torn by being pushed too wide. Especially, if the inner corehas a coefficient of thermal expansion of not less than 2.0×10⁻⁶/K andnot more than 5.0×10⁻⁶/K, it is possible to sufficiently straighten sagwithout causing the film to suffer from a tearing defect.

In terms of heat resistance, it is preferable that the inner core bemade of graphite, in particular an extrusion molded product, a moldedproduct, a CIP molded product, or the like.

(Accuracy of the Diameter of the Inner Core)

The accuracy of the diameter of the inner core can be expressed by thefollowing equation:Accuracy of Diameter (%)=(Maximum Value of Outer Perimeter−Minimum Valueof Outer Perimeter)/Minimum Value of Outer Perimeter×100where the maximum and minimum values of the outer perimeter of the innercore are each a value of the outer perimeter of the inner core aroundwhich the raw graphite film is being wound.

A method for measuring the outer perimeter of the inner core is suchthat measurements are performed by a method capable of measurements withsuch accuracy as a resolution of not more than 0.2 μm. For example,high-accuracy measurements are possible with a three-dimensionalmeasuring machine (Model: UPMC 850 CARAT Ultra) available from TokyoSeimitsu Co., Ltd.

The accuracy of the diameter of the inner core that is used in the thirdembodiment of the present invention is not more than 0.0426%, preferablynot more than 0.0107%, more preferably not more than 0.0027%, even morepreferably not more than 0.0006%, or especially preferable 0.0000%. Ifthe accuracy of the diameter is not more than 0.0426%, the resultinggraphite film is flack with sag of 20 mm or less.

(Rewinding Step)

In the execution of the straightening process step with a raw graphitefilm wound around the inner core, it is preferable that the raw graphitefilm be tightly wound around the inner core. Therefore, in the thirdembodiment of the present invention, a rewinding step of winding a rawgraphite film around the inner core be included prior to the executionof the straightening process. In the rewinding step, a rewindingapparatus can be used. In the rewinding step, it is preferable that theraw graphite film be wound with its ends aligned, because doing soallows force from the inner core to be evenly transmitted in thestraightening process. This leaves no place on the film where thepressure is not transmitted, thus enhancing the effect of thestraightening process. It is possible to align the ends by using an edgeposition control (control apparatus which automatically carries out anoperation of uniformly aligning film edges, so-called “ends”).Alternatively, as shown in FIG. 28, it is also possible to use avertical rewinding apparatus to rewind the film with its ends aligned.The rewinding work is facilitated by fixing the raw graphite film ontothe inner core with a double-sided adhesive tape and then starting towind the raw graphite film.

The strength of tight winding in the third embodiment of the presentinvention is the product of the torque of the rotating shaft of the coreand the outermost radius of a roll of raw graphite film (see FIG. 28).The raw graphite film is tightly wound until the stoppage of rotation ofthe rotating shaft by rotating the rotating shaft at a predeterminedtorque with the raw graphite film fixed so that the outermostcircumference does not move. For example, if the radius of the innercore of the raw graphite film of FIG. 28 is 50 mm, the winding thickness2610 of the raw graphite film is 5 mm, and the torque of the rotatingshaft 4N·m, the strength of tight winding is 220 N·m/m.

The strength of tight winding in the rewinding step in the thirdembodiment of the present invention is not less than 1 N·m/m, preferablynot less than 5 N·m/m, more preferably not less than 10 N·m/m, even morepreferably not less than 100 N·m/m, or especially preferably not lessthan 200 N·m/m. With a strength of tight winding of not less than 1N·m/m, the force of expansion of the inner core is transmitted to theouter circumference of the roll of raw graphite film, so that theresulting graphite film has improved flatness. In particular, with astrength of tight winding of not less than 200 N·m/m, the resultinggraphite film has sufficiently improved flatness.

(Method for Fixing Ends)

In a case where the straightening process is carried out with a rawgraphite film wound around the inner core, the straightening effect ishardly brought about if the raw graphite film is loosened from the innercore during the heat treatment. Therefore, it is necessary to fixedlywind a raw graphite film so that the raw graphite film is not loosened.A possible example of doing so is to prevent loosening by placing on theoutermost circumference of a raw graphite film wound around the innercore. Another possible example is to simply placing a wound raw graphitefilm sideways so that the raw graphite film is fixed by its own weightin a way that it does not get loosened. Still another possible exampleis to fix a raw graphite film by stretching it by the outermostperipheral ends. Furthermore, an effective example is to suppressloosening while controlling the pressure under which a raw graphite filmis fixed. Any fixing method may be employed unless the winding getsloosened.

<Length and Widths of a Graphite Film>

The width of a graphite film means the length of a shorter side of acontinuous sheet of graphite film. The width of a graphite film in thethird embodiment of the present invention is not particularly limited.However, with a greater width, the effect of sag control by thestraightening process step can be remarkably exhibited, as a greaterwidth makes it more difficult to control sag. The width of a graphitefilm in the third embodiment of the present invention is preferably notless than 100 mm, more preferably not less than 200 mm, or even morepreferably not less than 400 mm. With a width of not less than 100 mm,the effect of sag control in the third embodiment of the presentinvention can be remarkably exhibited.

The length of a graphite film means the length of a longer side of acontinuous sheet of graphite film. The length of a raw graphite film inthe third embodiment of the present invention is not particularlylimited. However, it is preferable to have a continuity of not less than4.0 m, more preferably not less than 10.0 m, or even more preferably20.0 m. A continuity of not less than 4.0 m makes it easy to carry outlamination, rewinding, etc.

Further, the continuity of graphite films having two different saggingshapes may be preferably not less than 2.0 m, more preferably not lessthan 5.0 mm, or even more preferably 10.0 mm. A continuity of not lessthan 2.0 mm makes it easy to carry out lamination, rewinding, etc.

<Polymer Film>

An example of a polymer film that is used in the third embodiment of thepresent invention is, but is not particularly limited to, a film of apolymer selected from the group consisting of polyimide (PI), polyamide(PA), polyoxadiazole (POD), polybenzooxazole (PBO), polybenzobisoxazole(PBBO), polythiazole (PT), polybenzothiazole (PBT), polybenzobisthiazole(PBBT), polyparaphenylenevinylene (PPV), polybenzoimidazole (PBI), andpolybenzobisimidazole (PBBI). Use of at least one of these polymersmakes it easy to obtain a raw graphite film and a graphite film that areexcellent in crystallinity, thermal diffusivity, and thermalconductivity. Use of polyimide is especially preferred. It should benoted that a polymer film taken as an example in the third embodiment ofthe present invention can of course be used in the first and secondembodiments of the present invention.

Thus far, the first to third embodiments of the present invention havebeen described. The term “sag” as used in the present invention isdefined below with reference to the drawings.

As shown in FIG. 40, the term “bilaterally asymmetric sag” refers to sagformed in a shape such that the graphite film has two different halveswith respect to a widthwise middle portion thereof.

As shown in FIG. 41, the term “bilaterally symmetric sag” refers to sagformed in a shape such that the graphite film has two equal halves withrespect to a widthwise middle portion thereof.

As shown in FIG. 42, the term “sag in a middle portion” refers to sagformed in a shape such that a graphite film is more sagging in thewidthwise middle portion than at the widthwise ends.

As shown in FIG. 43, the term “sag of not more than 4.9 mm” refers tosag in a shape such that the deepest sag in the whole area extendingacross the width of the graphite film is not more than 4.9 mm.

As shown in FIG. 44, the term “sag lying at one end” refers to a sag ina shape such that the graphite film has a sag lying at one widthwise endthereof.

As shown in FIG. 45, the term “sag of not more than 20 mm” refers to sagin a shape such that the largest sag in the whole area extending acrossthe width of the graphite film is not more than 20 mm.

The present invention is not limited to the description of theembodiments above, but may be altered by a skilled person within thescope of the claims. An embodiment based on a proper combination oftechnical means disclosed in different embodiments is encompassed in thetechnical scope of the present invention.

EXAMPLES

The following description will discuss various Examples of the presentinvention and several Comparative Examples.

Examples A According to First Embodiment

<Conditions for Measurement of Various Physical Properties>

<Physical Properties of Polymer Film>

<Birefringence>

A birefringence of each polymer film was measured by using a Metricon'srefractive index and film thickness measuring system (Model: 2010 PRISMCOUPLER). The measurement was carried out by measuring refractiveindices of the polymer film in TE and TM modes, respectively, with useof a light source at a wavelength of 594 nm in an atmosphere having atemperature of 23° C. and a humidity of 50% and obtaining the value ofTE−TM as the birefringence.

<Physical Properties of Polymer Film after Sag Controlling Step>

<Cracking (Paper Tube Wrap-around Test)>

Evaluation was carried out to determine how each polymer film havingbeen subjected to the sag controlling step was prone to cracking. Theevaluation was carried out in the following manner: (i) a polymer filmhaving been subjected to the sag controlling step was kept in anatmosphere having a temperature of 23° C. and a humidity of 50% for 24hours, (ii) after that, the polymer film was wrapped around paper tubesof various diameters five turns each with a tensile strength of 30kgf/cm² in an atmosphere having a temperature of 23° C. and a humidityof 50%, and (iii) whether the polymer film cracked or not was checked.The evaluation criteria are as follows. The polymer film was rated as:“A” if it did not crack even when wrapped around a 1-in. diameter papertube; “B” if it cracked when wrapped around a 1-in. diameter paper tubebut did not crack when wrapped around a 1.5-in. diameter paper tube; “C”if it cracked when wrapped around a 1.5-in. diameter paper tube but didnot crack when wrapped around a 2-in. diameter paper tube; “D” if itcracked when wrapped around a 2-in. diameter paper tube but did notcrack when wrapped around a 3-in. diameter paper tube; and “E” if itcracked even when wrapped around a 3-in. diameter paper tube.

<Weight Loss Rate, Weight Retention Rate>

The actual weight loss rate and weight retention rate, which arerepresented by the following equations, of each polymer film immediatelyafter the sag controlling step were measured. A polymer film, and apolymer film immediately after the sag controlling step, were each cutinto a piece of 50 mm, and allowed to stand for 24 hours in anenvironment having a temperature of 23° C. and a humidity of 50%, andtheir weights were measured with the use of Aspro electronic balance(model no.: ASP213, available from AS ONE Corporation) in an environmenthaving a temperature of 23° C. and a humidity of 50%. The weight lossrate and the weight retention rate were calculated from the followingequations:Weight loss rate (%)=(Initial Weight of polymer film−Weight of polymerfilm immediately after sag controlling step)/Initial Weight of polymerfilm×100Weight retention rate (%)=100−Weight loss rate (%)

<Total Transmittance>

The total transmittances of a polymer film and of a polymer film havingbeen subjected to the sag controlling step were measured in thefollowing manner: (i) each polymer film was kept in an atmosphere havinga temperature of 23° C. and a humidity of 50% for 24 hours andthereafter (ii) the total transmittance was measured in an atmospherehaving a temperature of 23° C. and a humidity of 50% with the use ofHaze Meter (model: NDH-300A) available from NIPPON DENSHOKU. Themeasurement was carried out three times and the mean was found, which isshown in Tables.

<Physical Properties of Graphite Film>

<Measuring Sag in Graphite Film in Accordance with JIS C2151>

Sag in each graphite film was evaluated by measuring the depth of sag onthe basis of the film windability evaluation in accordance with JISC2151, in the following manner: (i) each film was kept in an atmospherehaving a temperature of 23° C. and a humidity of 50% for 24 hours andthereafter (ii) the depth of sag was measured in an atmosphere having atemperature of 23° C. and a humidity of 50%.

(Test Piece) A fresh test piece having a length of approximately 2 mdrawn from a roll of a graphite film is used. In this process, the testpiece is taken from around the center of the wound roll of the film. Forexample, in the case of a roll of 10 m, a test piece is taken fromaround 5 m away from the roll end.

(Apparatuses) Apparatuses employed will be described in the following(FIG. 2).

a) Mount Equipped with Rolls

The apparatus includes two freely-rotatable metallic rolls and a rigidmount that supports the two rolls in parallel. Each of the rolls has adiameter of 100 mm±10 mm, and has a length to such an extent that amaximum width of the film to be tested can be sufficiently placed on therolls. Axes of the two rolls are aligned in one horizontal plane and arefixed in parallel at a spacing of 1500 mm±15 mm within 0.1 degree (i.e.within 1.8 mm per meter of the roll's length). Each of the rolls has acylindrical shape having a cylindricity of not greater than 0.1 mm, andhas a surface subjected to appropriate pearskin finishing (not subjectedto abrasive finishing).

b) Device for Applying Tensile Force to Film

The apparatus enables the film freely hanging down from a second roll(roll 2) to be fixed to a weight or a spring-joint clamp at an oppositeend of the mount. The apparatus enables a load of 50 g per cm of thewidth of the film to be applied with the weight or spring, and adjusts atensile force to be applied as uniformly as possible in the widthwisedirection of the film. Alternatively, the film may be wrapped around atension roll, and a uniform tensile force of 50 g per cm of the widthmay be applied thereto.

c) Tools for Measuring Dimension

Tools used here are those by which a distance from a plane between thetwo rolls to the film sagged downward is measured at a midpoint betweenthe two rolls along a line parallel to the rolls. The tools for use inthe measurement are a steel straightedge ruler having a length of notless than 1525 mm and a steel graduated ruler having a length of 150 mmand being marked with 1 mm increments. Alternatively, a complex devicemay be used that indicates the position of the film automatically orsemiautomatically.

(Measurement Procedure) As shown in FIG. 2, a test piece is placed in alength direction on two rolls of the apparatus. A tensile force (50 gper cm as described earlier) is applied to the free end of the film. Afinal position of the film that passes over the roll 2 is adjusted suchthat the film becomes nearly level in the middle of the two rolls.

Using the steel straightedge ruler and the steel graduated ruler, thefilm is checked along the widthwise direction at the midpoint betweenthe two rolls.

(Results) The film was visually checked to find which portion had thedeepest sag, and that portion was measured for depth of sag. Theobtained value was used as sag Zgs. This result is shown in Tables.

<How to Measure Sag a-Value at End>

The measurement of the sag a-value of each graphite film at its edgeswas also carried out after the film was set in the same state as in theabove-described sag measurement in accordance with JIS C2151. As shownin FIG. 9, a depth of sag at the outer edge of the film from a suspendedline was measured, and a depth of sag at the point 30 mm away from theouter edge of the film from the suspended line was then measured.Thereafter, (a depth of sag at the point 30 mm away from the outer edge)was subtracted from (a depth of sag at the outer edge). For the rightand left edges of the film, the same measurement was carried out, andthe mean of the obtained two measurements for the right and left edgeswas used as a measured value. Measured values are shown in Tables.

<How to Measure Sag b-Value in Middle Portion>

The measurement of the sag b-value of each graphite film in a middleportion was also carried out after the film was set in the same state asin the above-described sag measurement in accordance with JIS C2151. Asillustrated in FIG. 10, sag in a widthwise middle portion of eachgraphite film was measured, and the obtained values are shown in Tables.

<Measurement of Camber of Graphite Film in Accordance with JIS C2151>

Camber of each graphite film was evaluated by measuring the degree ofcamber on the basis of the film windability evaluation in accordancewith JIS C2151, in the following manner: (i) each film was kept in anatmosphere having a temperature of 23° C. and a humidity of 50% for 24hours and thereafter (ii) the degree of camber was measured in anatmosphere a temperature of 23° C. and a humidity of 50%. The film in agiven length is unrolled and placed on a plane, and each deviation fromthe straight line is measured for both edges of the film.

(Apparatus) Apparatuses employed will be described in the following(FIG. 11).

a) Table

The table employed has a width sufficiently greater than the maximumwidth of the film to be tested, a length of 1500 mm±15 mm, and a degreeof parallelization at both ends being not greater than 0.1 degree (ornot greater than 1.8 mm/m of the width of the table). The surface shouldbe flat and horizontal which has been subjected to pearskin finishingwith an appropriate material (not subjected to abrasive finishing). Whenthe table has a greater length than that defined, two parallel referencelines with an interval of 1500 mm±15 mm should be clearly marked on thesurface of the table. The degree of parallelization of the referencelines is to be not greater than 0.1 degree (i.e., not greater than 1.8mm/m of the length of the reference line).

b) Brush

A soft brush for flattening the film placed on the surface of the table.

c) Straightedge Ruler

A steel ruler having a length of not less than 1525 mm.

d) Graduated Ruler

A steel graduated ruler having a length of 150 mm and being marked with1 mm increments.

(Test Piece) A fresh test piece having a length of approximately 2 mdrawn from a roll of a graphite film is used. In this process, the testpiece is taken from around the center of the wound roll of the film.More specifically, in the case of a roll of 10 m, a test piece is takenfrom around 5 m away from the roll end.

(Measurement Procedure) The test piece is placed on the table along alongitudinal direction as shown in FIG. 11. The film is gently brushedwith weak force from one end to allow the test piece to be in closecontact with the table such that trapped air does not remain as far aspossible.

An edge of the straightedge ruler is placed along one edge of the filmsuch that the deviation of the film edge from the straight line can bewell observed. The steel straightedge ruler is adjusted so as to agreewith the edges of the film at both ends of the table (or on referenceline). Nearly in the middle between the reference positions, deviationd₁ of the film edge from the steel straightedge ruler is measured at aminimum scale of 1 mm using the steel graduated ruler. Deviation d₂ ofthe other edge of the film from the straightedge ruler is also measuredin the same way.The camber value of the test piece is determined as the sum (d₁+d₂) ofdeviations of the film edge from the edge of the straightedge rulerrepresented by millimeters at both ends of the film in the middle of theinterval between the reference lines.

(Result) The sum (d₁+d₂) of the deviations is used as a characteristicvalue of camber. The values are shown in Tables.

<Sag Reproducibility>

Sag reproducibility was evaluated. In each of Examples, ComparativeExamples and Reference Examples, five samples were measured for theirsag Zgs so that the number of evaluations was n=5. The differencebetween the maximum and minimum values of the sag Zgs was found. Whenthe difference between the maximum and minimum values of the sag Zgs wasless than 10 mm, then the sag Zgs was rated as “A”. When the differencewas not less than 10 mm and less than 20 mm, then the sag Zgs was ratedas “B”. When the difference was not less than 20 mm and less than 30 mm,then the sag Zgs was rated as “C”. When the difference was not less than30 mm and less than 40 mm, then the sag Zgs was rated as “D”. When thedifference was equal to or greater than 40 mm, then the sag Zgs wasrated as “E”.

<Resistance to Tearing>

A rewinding test was carried out to evaluate tears that may occur duringthe test. The rewinding test was carried out in the following manner: agraphite film wrapped around a 3-in. diameter first paper tube wasrewound around a 3-in. diameter second paper tube placed in parallelwith the first paper tube (see FIG. 12). The distance between the firstand second paper tubes was 300 mm. The tensile force to be applied inthe MD direction of the graphite film was 30 g/cm, and the rewindingspeed was 1 m/min.

The following describes a method for evaluating tears of graphite filmsin the rewinding test. After the rewinding test, across the whole areaof the film, tears of not less than 5 mm were counted and converted asthe number of visible tears across the width of the film per unitlongitudinal length (1 m). The graphite films were rated as: “A” whenthe number of tears per meter was 0; “B” when the number of tears permeter was greater than 0 and less than 0.05; “C” when the number oftears per meter was not less than 0.05 and less than 0.2; “D” when thenumber of tears per meter was not less than 0.2 and less than 1; and “E”when the number of tears per meter was not less than 1.

The results are expressed as “best evaluation value−worst evaluationvalue”. In a case where the best and worst evaluations are the same, theresult is shown as a single evaluation value.

<Lamination Property>

A laminating test as illustrated in FIG. 13 was carried out. Morespecifically, each graphite film, which was wrapped around a 3-in.diameter paper tube, was bonded to PET tape 10 μm in thickness and 150mm in width by continuously supplying the graphite film between a firstroll having an outer diameter of 50 mm and a length of 635 mm and asecond roll of the same size which was parallel to the first roll. Thegraphite film was continuously supplied between the first roll and thesecond roll so that the angle formed by a line connecting (the startingpoint of contact between the first roll and the graphite film) and (thecenter point of the first roll) and a line connecting (the center pointof the first roll) and (the point of contact between the first roll andthe second roll) was 120 degrees (see FIG. 14). The PET tape was 633Kavailable from Teraoka Seisakusho Co., Ltd. The PET tape was supplied tothe second roll so that the angle formed by a line connecting (thestarting point of contact between the second roll and the PET tape) and(the center point of the second roll) and a line connecting (the centerpoint of the second roll) and (the point of contact between the firstroll and the second roll) was 120 degrees. The tensile force to beapplied in the MD direction of the graphite film was 30 g/cm, and therewinding speed was 1 m per minute.

Wrinkles (as shown in FIG. 15) of the graphite films after thecompletion of the laminating test were evaluated as follows. Across thewhole area of a roll of the film, wrinkles of not less than 5 mm inlength were counted and converted as the number of visible wrinklesacross the width of the film per unit longitudinal length (1 m). Thegraphite films were rated as: “A” when the number of wrinkles per meterwas 0; “B” when the number of wrinkles per meter was greater than 0 andless than 0.05; “C” when the number of wrinkles per meter was not lessthan 0.05 and less than 0.2; “D” when the number of wrinkles per meterwas not less than 0.2 and less than 1; and “E” when the number ofwrinkles per meter was not less than 1.

The results are expressed as “best evaluation value−worst evaluationvalue”. In a case where the best and worst evaluations are the same, theresult is shown as a single evaluation value.

Example 1A

A polymer film used here was a polyimide film Apical NPI (available fromKaneka Corporation) having a birefringence of 0.14, thickness of 75 μm,width of 200 mm and length of 10 m. In Apical NPI, temperaturescorresponding to the weight loss rates 1.0%, 1.1%, 2.8%, 10.0%, 15.0%and 20.0% in the measurement method of the present invention are 500°C., 520° C., 550° C., 580° C., 600° C., 630° C. and 655° C.,respectively. The polymer film was set to a rewinding apparatus asillustrated in FIG. 8, and the sag controlling step was carried outwhile the polymer film was continuously supplied to a heat treatmentapparatus. The length of the heat treatment apparatus along the MDdirection was 60 cm and the length along the TD direction was 30 cm. Thetemperature in a widthwise middle portion of the polymer film wascontrolled such that (i) the temperature at an entrance of the heattreatment apparatus was 500° C. (corresponding to the startingtemperature of thermal decomposition of the polymer film used in thepresent example), (ii) the temperature in a position 50 cm away from theentrance was the maximum temperature 580° C. (corresponding to the sagcontrolling temperature for the polymer film used in the presentexample), and (iii) the temperature at an exit, which is 10 cm away fromthe position of the maximum temperature, was 500° C. A lineartemperature gradient was given so that the widthwise middle portion ofthe polymer film had a temperature distribution along the lengthwisedirection of the polymer film as shown in FIG. 8. The line speed wascontrolled so that the actual temperature of the polymer film wouldincrease at 80° C. per minute (equivalent to a line speed of 50 cm perminute) in the 500° C.-580° C. range. Furthermore, a linear temperaturegradient was given also along the widthwise direction so that (i) eachof the temperatures at both widthwise ends (each of which is 10 cm awayfrom the widthwise middle portion) of the polymer film was 1° C. higherthan the temperature in the widthwise middle portion of the polymer filmand (ii) the polymer film had a temperature distribution along thewidthwise direction of the polymer film as shown in FIG. 8. Thetemperature gradient along the widthwise direction was measured in fourpositions, i.e., the positions where the temperatures in the widthwisemiddle portion of the polymer film were 500° C., 530° C., 560° C. and580° C., respectively. It was confirmed that, in each of the fourpositions, each of the temperatures at the widthwise ends was 1° C.higher than the temperature in the widthwise middle portion.

The polymer film was conveyed while a tensile force was applied to thefilm with a tensile strength of 30 kgf/cm². In the heat treatmentapparatus, the film was conveyed through a gap between graphite jigsplaced above and below the film (see FIG. 8). A pressure of 2 g/cm² wasapplied to the film in its thickness direction. After the sagcontrolling step, the film was evaluated for cracking and was measuredfor the weight retention rate, weight loss rate, and totaltransmittance.

Next, the film having been subjected to the sag controlling step wascooled to room temperature (23° C.), was wound into a roll having aninner diameter of 100 mm, and was set in a carbonizing furnace such thatthe widthwise direction of the film was parallel to the verticaldirection (see FIG. 16). The film was carbonized by heat treatment whileraising the temperature in the carbonizing furnace from room temperatureto 1400° C. at a temperature rise rate of 2° C. per minute withoutparticular control of the temperatures at the both widthwise ends of thefilm and the temperature in the widthwise middle portion of the film.

Next, the carbonized film was cooled to room temperature, was set in agraphitization furnace in the same manner as in the carbonization, andwas graphitized by heat treatment while raising the temperature in thegraphitization furnace from room temperature to 2900° C. at 0.5° C. perminute without particular control of the temperatures at the bothwidthwise ends of the film and the temperature in the widthwise middleportion of the film.

Next, the graphitized film was cooled to room temperature, andcompressed with a pressure of 10 MPa at room temperature.

Five films were produced in the same manner so that the number ofevaluations was n=5, and were evaluated for their sag reproducibility,sag Zgs, a-value, b-value, camber, resistance to tearing, and laminationproperty. As for the sag Zgs, a-value, b-value and camber, their maximumand minimum values of the five (n=5) evaluations are shown in Tables 1A,2A, 3A and 4A. The resistance to tearing and lamination property areshown in Tables 1A, 2A, 3A and 4A as “best evaluation value−worstevaluation value”. It should be noted that, in a case where the best andworst evaluations are the same, the result is shown as a singleevaluation value.

Example 2A

A graphite film was produced in the same manner as that described inExample 1A, except that a linear temperature gradient along thewidthwise direction was such that each of the temperatures at bothwidthwise ends of a polymer film was 3° C. higher than the temperaturein a widthwise middle portion of the polymer film. The variousproperties of the graphite film were evaluated. The results are shown inTables 1A, 2A, 3A and 4A.

Example 3A

A graphite film was produced in the same manner as that described inExample 1A, except that a linear temperature gradient along thewidthwise direction was such that each of the temperatures at bothwidthwise ends of a polymer film was 5° C. higher than the temperaturein a widthwise middle portion of the polymer film. The variousproperties of the graphite film were evaluated. The results are shown inTables 1A, 2A, 3A and 4A.

Example 4A

A graphite film was produced in the same manner as that described inExample 1A, except that a linear temperature gradient along thewidthwise direction was such that each of the temperatures at bothwidthwise ends of a polymer film was 10° C. higher than the temperaturein a widthwise middle portion of the polymer film. The variousproperties of the graphite film were evaluated. The results are shown inTables 1A, 2A, 3A and 4A.

Example 5A

A graphite film was produced in the same manner as that described inExample 1A, except that a linear temperature gradient along thewidthwise direction was such that each of the temperatures at bothwidthwise ends of a polymer film was 20° C. higher than the temperaturein a widthwise middle portion of the polymer film. The variousproperties of the graphite film were evaluated. The results are shown inTables 1A, 2A, 3A and 4A.

Example 6A

A graphite film was produced in the same manner as that described inExample 3A, except that a linear temperature gradient along thewidthwise direction was such that the temperature at an end 1, which isone of both widthwise ends of a polymer film, was 5° C. higher than thetemperature in a widthwise middle portion of the polymer film and thetemperature at an end 2, which is the other of the both widthwise ends,was 3° C. higher than the temperature in the widthwise middle portion ofthe polymer film. The various properties of the graphite film wereevaluated. The results are shown in Tables 1A, 2A, 3A and 4A.

Example 7A

A graphite film was produced in the same manner as that described inExample 3A, except that, in the sag controlling step, the maximumtemperature in the heat treatment apparatus was 555° C. and the lengthof the furnace and the line speed were adjusted so that the temperaturerise rate was 80° C. per minute. The various properties of the graphitefilm were evaluated. The results are shown in Tables 1A, 2A, 3A and 4A.

Example 8A

A graphite film was produced in the same manner as that described inExample 3A, except that, in the sag controlling step, the maximumtemperature in the heat treatment apparatus was 605° C. and the lengthof the furnace and the line speed were adjusted so that the temperaturerise rate was 80° C. per minute. The various properties of the graphitefilm were evaluated. The results are shown in Tables 1A, 2A, 3A and 4A.

Example 9A

A graphite film was produced in the same manner as that described inExample 3A, except that, in the sag controlling step, the maximumtemperature in the heat treatment apparatus was 630° C. and the lengthof the furnace and the line speed were adjusted so that the temperaturerise rate was 80° C. per minute. The various properties of the graphitefilm were evaluated. The results are shown in Tables 1A, 2A, 3A and 4A.

Example 10A

A graphite film was produced in the same manner as that described inExample 3A, except that, in the sag controlling step, the maximumtemperature in the heat treatment apparatus was 655° C. and the lengthof the furnace and the line speed were adjusted so that the temperaturerise rate was 80° C. per minute. The various properties of the graphitefilm were evaluated. The results are shown in Tables 1A, 2A, 3A and 4A.

Example 11A

A graphite film was produced in the same manner as that described inExample 3A, except that (i) in the sag controlling step, the maximumtemperature in the heat treatment apparatus was 700° C. (sag controllingtemperature was 655° C.) and the length of the furnace and the linespeed were adjusted so that the temperature rise rate was 80° C. perminute and (ii) the carbonization step was not carried out. The variousproperties of the graphite film were evaluated. The results are shown inTables 1A, 2A, 3A and 4A.

Example 12A

A graphite film was produced in the same manner as that described inExample 3A, except that (i) in the sag controlling step, the maximumtemperature in the heat treatment apparatus was 900° C. (sag controllingtemperature was 655° C.) and the length of the furnace and the linespeed were adjusted so that the temperature rise rate was 80° C. perminute and (ii) the carbonization step was not carried out. The variousproperties of the graphite film were evaluated. The results are shown inTables 1A, 2A, 3A and 4A.

Example 13A

A graphite film was produced in the same manner as that described inExample 3A, except that the raw material for the graphite film was apolyimide film Apical AH (available from Kaneka Corporation) having abirefringence of 0.10, thickness of 75 μm, width of 200 mm and length of10 m in which the temperatures corresponding to the weight loss rates1.0%, 1.1%, 2.8%, 10.0%, 15.0% and 20.0% in the measurement method ofthe present invention were 500° C., 520° C., 550° C., 580° C., 600° C.,630° C. and 655° C., respectively. The various properties of thegraphite film were evaluated. The results are shown in Tables 1A, 2A, 3Aand 4A.

Example 14A

A polyimide film Apical NPI (available from Kaneka Corporation) having abirefringence of 0.14, thickness of 75 μm, width of 200 mm and length of2 m was wrapped around a graphite jig having an outer diameter of 100 mm(see FIG. 7), the rolled polyimide film was set in a heat treatmentapparatus horizontally, and the sag controlling step was carried out. Aheat treatment was carried out under the condition in which (i) a lineartemperature gradient along the widthwise direction was given so thateach of the temperatures at both widthwise ends (each of which is 10 cmaway from the widthwise middle portion) of the polymer film was 5° C.higher than the temperature in a widthwise middle portion of the polymerfilm (see FIG. 7) and (ii) the temperature in the widthwise middleportion of the polymer film was controlled so as to increase at 2° C.per minute in the 500° C.-580° C. range. The temperature gradient alongthe widthwise direction was measured when the temperature in thewidthwise middle portion of the polymer film was 500° C., 530° C., 560°C. and 580° C. Both the temperatures at the widthwise ends of the filmand the temperature in the widthwise middle portion of the film weremeasured in four positions, which are angularly displaced 90 degreesfrom each other, of the polymer film rolled in a cylindrical form (seeFIG. 7). It was confirmed that each of the temperatures at the widthwiseends was 5° C. higher than the temperature in the widthwise middleportion, in any of the four positions under any of the four differenttemperature conditions.

A graphite film was produced in the same manner as that described inExample 3A, except for the above conditions. The various properties ofthe graphite film were evaluated. The results are shown in Tables 1A,2A, 3A and 4A.

Example 15A

A graphite film was produced in the same manner as that described inExample 14A, except that the raw material for the graphite film was apolyimide film Apical AH (available from Kaneka Corporation) having abirefringence of 0.10, thickness of 75 μm, width of 200 mm and length of10 m. The various properties of the graphite film were evaluated. Theresults are shown in Tables 1A, 2A, 3A and 4A.

Example 16A

As illustrated in FIG. 6, a polyimide film Apical NPI (available fromKaneka Corporation) having a birefringence of 0.14, thickness of 75 μm,width of 200 mm and length of 0.7 m was placed on a graphite hearth, anda heavy graphite plate was placed on the film so that a load of 5 g/cm²was imposed on the film. As illustrated in FIG. 6, thermocouples wereprovided along the lengthwise direction at intervals of 100 mm. A heattreatment was carried out under the condition in which (i) a lineartemperature gradient along the widthwise direction was given so thateach of the temperatures at both widthwise ends of the film was 5° C.higher than the temperature in a widthwise middle portion of the polymerfilm as shown in FIG. 6 and (ii) the temperature in the widthwise middleportion of the polymer film was controlled so as to increase at thetemperature rise rate of 2° C. per minute in the 500° C.-580° C. range.The temperature gradient along the widthwise direction was measured whenthe temperature in the widthwise middle portion of the polymer film was500° C., 530° C., 560° C. and 580° C. It was confirmed that each of thetemperatures at the both widthwise ends of the film was 5° C. higherthan the temperature in the widthwise middle portion of the film, in anyof seven positions under any of the four different temperatureconditions. A graphite film was produced in the same manner as thatdescribed in Example 14A, except that the carbonization step and thegraphitization step were carried out by holding the film in the samemanner as in the sag controlling step of the present example. Thevarious properties of the graphite film were evaluated. The results areshown in Tables 1A, 2A, 3A and 4A.

Example 17A

A graphite film was produced in the same manner as that described inExample 16A, except that the raw material for the graphite film was thepolyimide film Apical AH (available from Kaneka Corporation) having abirefringence of 0.10, thickness of 75 μm, width of 200 mm and length of10 m. The various properties of the graphite film were evaluated. Theresults are shown in Tables 1A, 2A, 3A and 4A.

Example 18A

A graphite film was produced in the same manner as that described inExample 1A, except that the linear temperature gradient along thewidthwise direction was such that each of the temperatures at bothwidthwise ends of a polymer film was 40° C. higher than the temperaturein a widthwise middle portion of the polymer film. The variousproperties of the graphite film were evaluated. The results are shown inTables 1A, 2A, 3A and 4A.

Example 19A

A graphite film was produced in the same manner as that described inExample 3A, except that (i) only for the sag controlling temperature580° C., a linear temperature gradient along the widthwise direction wasgiven so that each of the temperatures at both widthwise ends of apolymer film was 5° C. higher than the temperature in a widthwise middleportion of the polymer film and (ii) in the other three positions, thetemperatures at the both widthwise ends and the temperature in thewidthwise middle portion were the same. The various properties of thegraphite film were evaluated. The results are shown in Tables 1A, 2A, 3Aand 4A.

Example 20A

A graphite film was produced in the same manner as that described inExample 3A, except that (i) only for the position of 530° C., a lineartemperature gradient along the widthwise direction was given so thateach of the temperatures at both widthwise ends of a polymer film was 5°C. higher than the temperature in a widthwise middle portion of thepolymer film and (ii) in the other three positions, the temperatures atthe both widthwise ends and the temperature in the widthwise middleportion were the same. The various properties of the graphite film wereevaluated. The results are shown in Tables 1A, 2A, 3A and 4A.

Example 21A

A graphite film was produced in the same manner as that described inExample 1A, except that a linear temperature gradient along thewidthwise direction was such that each of the temperatures at bothwidthwise ends of a polymer film was 0.5° C. higher than the temperaturein a widthwise middle portion of the polymer film. The variousproperties of the graphite film were evaluated. The results are shown inTables 1A, 2A, 3A and 4A.

Example 22A

A graphite film was produced in the same manner as that described inExample 3A, except that the compression after the graphitization was notcarried out. The various properties of the graphite film were evaluated.The results are shown in Tables 1A, 2A, 3A and 4A.

TABLE 1A Raw Material Film Thickness Width Length Type Birefringence μmmm m Example 1A NPI 0.14 75 200 10 Example 2A NPI 0.14 75 200 10 Example3A NPI 0.14 75 200 10 Example 4A NPI 0.14 75 200 10 Example 5A NPI 0.1475 200 10 Example 6A NPI 0.14 75 200 10 Example 7A NPI 0.14 75 200 10Example 8A NPI 0.14 75 200 10 Example 9A NPI 0.14 75 200 10 Example 10ANPI 0.14 75 200 10 Example 11A NPI 0.14 75 200 10 Example 12A NPI 0.1475 200 10 Example 13A AH 0.10 75 200 10 Example 14A NPI 0.14 75 200 2Example 15A AH 0.10 75 200 2 Example 16A NPI 0.14 75 200 0.7 Example 17AAH 0.10 75 200 0.7 Example 18A NPI 0.14 75 200 10 Example 19A NPI 0.1475 200 10 Example 20A NPI 0.14 75 200 10 Example 21A NPI 0.14 75 200 10Example 22A NPI 0.14 75 200 10

TABLE 2A Sag Controlling Step Max Number of Starting Temp Temp NumberMeasure- Temp of Thermal Sag Temp in of ment Rise DecompositionControlling Temp Gradient Heat Measure- Positions Pulling Rate End 1Middle End 2 End 1 Middle End 2 Max Mn Treat- ment Satisfying StrengthLoad ° C./ Method ° C. ° C. ° C./m ment Positions Conditions kgf/cm2g/cm2 min Example 1A CLFPM*1 501 500 501 581 580 581 5 5 580 4 4 30 2 80Example 2A CLFPM*1 503 500 503 583 580 583 15 15 580 4 4 30 2 80 Example3A CLFPM*1 505 500 505 585 580 585 25 25 580 4 4 30 2 80 Example 4ACLFPM*1 510 500 510 590 580 590 50 50 580 4 4 30 2 80 Example 5A CLFPM*1520 500 520 600 580 600 100 100 580 4 4 30 2 80 Example 6A CLFPM*1 505500 505 585 580 583 25 15 580 4 4 30 2 80 Example 7A CLFPM*1 505 500 505560 555 560 25 25 555 3 3 30 2 80 Example 8A CLFPM*1 505 500 505 610 605610 25 25 605 5 5 30 2 80 Example 9A CLFPM*1 505 500 505 635 630 635 2525 630 6 6 30 2 80 Example 10A CLFPM*1 505 500 505 660 655 660 25 25 6557 7 30 2 80 Example 11A CLFPM*1 505 500 505 660 655 660 25 25 700 7 7 302 80 Example 12A CLFPM*1 505 500 505 660 655 660 25 25 900 7 7 30 2 80Example 13A CLFPM*1 505 500 505 585 580 585 25 25 580 4 4 30 2 80Example 14A CBM*2 505 500 505 585 580 585 25 25 580 4 4 Not Not  2Available Available Example 15A CBM*2 505 500 505 585 580 585 25 25 5804 4 Not Not  2 Available Available Example 16A SBM*3 505 500 505 585 580585 25 25 580 4 4 Not 5  2 Available Example 17A SBM*3 505 500 505 585580 585 25 25 580 4 4 Not 5  2 Available Example 18A CLFPM*1 540 500 540620 580 620 200 200 580 4 4 30 2 80 Example 19A CLFPM*1 Starting Temp ofThermal 25 25 580 1 1 30 2 80 Decomposition: 500° C. Sag ControllingTemp: 580° C. Only for 580° C. each end is 5° C. higher than middleportion. Example 20A CLFPM*1 Starting Temp of Thermal 25 25 580 1 1 30 280 Decomposition: 500° C. Sag Controlling Temp: 580° C. Only for 530° C.each end is 5° C. higher than middle portion. Example 21A CLFPM*1 500.5500 500.5 580.5 580 580.5 2.5 2.5 580 4 4 30 2 80 Example 22A CLFPM*1505 500 505 585 580 585 25 25 580 4 4 30 2 80 *1CLFPM stands for“continuous long film processing method”. *2CBM stands for “cylindricalbatch method”. *3SBM stands for “sheet batch method”.

TABLE 3A Physical Properties of Film Carbonization Step After SagControlling Step Width- Cracking wise Graphitization Step (Paper Differ-Temp Temp Tube Weight Weight Total ence Rise Rise Wrap- Retention LossTransmit- Max of Rate Max Rate around Rate Rate tance Method of TempFilm ° C./ Method of Temp ° C./ Test) % % % Setting ° C. ° C. minSetting ° C. min Compression Example 1A A 97.2 2.8 0.20 Cylindrical Roll1400 0 2 Cylindrical Roll 2900 0.5 Carried Out Example 2A A 97.2 2.80.20 Cylindrical Roll 1400 0 2 Cylindrical Roll 2900 0.5 Carried OutExample 3A A 97.2 2.8 0.20 Cylindrical Roll 1400 0 2 Cylindrical Roll2900 0.5 Carried Out Example 4A A 97.2 2.8 0.20 Cylindrical Roll 1400 02 Cylindrical Roll 2900 0.5 Carried Out Example 5A A 97.2 2.8 0.20Cylindrical Roll 1400 0 2 Cylindrical Roll 2900 0.5 Carried Out Example6A A 97.2 2.8 0.20 Cylindrical Roll 1400 0 2 Cylindrical Roll 2900 0.5Carried Out Example 7A A 98.8 1.2 5.50 Cylindrical Roll 1400 0 2Cylindrical Roll 2900 0.5 Carried Out Example 8A A 90.0 10.0 0.03Cylindrical Roll 1400 0 2 Cylindrical Roll 2900 0.5 Carried Out Example9A B 85.0 15.0 — Cylindrical Roll 1400 0 2 Cylindrical Roll 2900 0.5Carried Out Example 10A C 80.0 20.0 — Cylindrical Roll 1400 0 2Cylindrical Roll 2900 0.5 Carried Out Example 11A D 62.0 38.0 — NotCarried Out Cylindrical Roll 2900 0.5 Carried Out Example 12A E 52.048.0 — Not Carried Out Cylindrical Roll 2900 0.5 Carried Out Example 13AA 97.2 2.8 0.20 Cylindrical Roll 1400 0 2 Cylindrical Roll 2900 0.5Carried Out Example 14A A 97.2 2.8 0.20 Cylindrical Roll 1400 0 2Cylindrical Roll 2900 0.5 Carried Out Example 15A A 97.2 2.8 0.20Cylindrical Roll 1400 0 2 Cylindrical Roll 2900 0.5 Carried Out Example16A A 97.2 2.8 0.20 Sheet Laminate 1400 0 2 Sheet Laminate 2900 0.5Carried Out Example 17A A 97.2 2.8 0.20 Sheet Laminate 1400 0 2 SheetLaminate 2900 0.5 Carried Out Example 18A A 97.2 2.8 0.20 CylindricalRoll 1400 0 2 Cylindrical Roll 2900 0.5 Carried Out Example 19A A 97.22.8 0.20 Cylindrical Roll 1400 0 2 Cylindrical Roll 2900 0.5 Carried OutExample 20A A 97.2 2.8 0.20 Cylindrical Roll 1400 0 2 Cylindrical Roll2900 0.5 Carried Out Example 21A A 97.2 2.8 0.20 Cylindrical Roll 1400 02 Cylindrical Roll 2900 0.5 Carried Out Example 22A A 97.2 2.8 0.20Cylindrical Roll 1400 0 2 Cylindrical Roll 2900 0.5 Not Carried Out

TABLE 4A Physical Properties of Graphitized Film Sag Sag a-Value b-ValueCamber Repro- Max Mn Max Mn Max Mn Max Mn Resistance Laminationducibility mm mm mm mm to Tearing Property Example 1A A 10 9 5 5 0 0 <2<2 C A Example 2A A 30 28 20 19 0 0 <2 <2 B A Example 3A A 40 38 30 29 00 <2 <2 A A Example 4A A 70 65 55 53 0 0 <2 <2 A B Example 5A A 90 85 7570 0 0 <2 <2 A C Example 6A A 40 38 30 28 0 0 3 <2 A C Example 7A B 3020 20 10 0 0 <2 <2 B A Example 8A A 45 43 32 30 0 0 <2 <2 A A Example 9AA 48 45 34 32 0 0 <2 <2 A A Example 10A A 50 48 35 33 0 0 <2 <2 A AExample 11A A 50 48 35 33 0 0 <2 <2 A A Example 12A A 50 48 35 33 0 0 <2<2 A A Example 13A A 40 38 30 28 0 0 <2 <2 A A Example 14A C 40 20 30 100 0 3 <2 A-B C Example 15A C 40 20 30 10 0 0 3 <2 A-B C Example 16A C 4020 30 10 0 0 Unmeasurable Unmeasurable A-B C Example 17A C 40 20 30 10 00 Unmeasurable Unmeasurable A-B C Example 18A A 120 111 95 89 0 0 <2 <2A D Exarrple 19A B 30 20 20 10 0 0 <2 <2 B A Example 20A C 25 5 20 0 0 0<2 <2 B-D A Example 21A A 5 5 3 3 0 0 <2 <2 D A Example 22A A 40 38 3029 0 0 <2 <2 A A

Comparative Example 1A

A polymer film, which had not been subjected to the sag controllingstep, was carbonized in the following manner. The polymer film used herewas a polyimide film Apical NPI (available from Kaneka Corporation)having a birefringence of 0.14, thickness of 75 μm, width of 200 mm andlength of 10 m. In the same manner as in Example 1A, the film was woundinto a roll having an inner diameter of 100 mm, was set in a carbonizingfurnace so that the widthwise direction of the film was parallel to thevertical direction (see FIG. 16), and was carbonized by heat treatmentwhile raising the temperature in the carbonizing furnace from roomtemperature (23° C.) to 1400° C. at 2° C./min without particular controlof the temperatures at both widthwise ends of the film and thetemperature in a widthwise middle portion of the film.

Next, the carbonized film was cooled to room temperature, was set in agraphitization furnace in the same manner as in the carbonization, andwas graphitized by heat treatment while raising the temperature in thegraphitization furnace from room temperature to 2900° C. at 0.5° C. perminute without particular control of the temperatures at the bothwidthwise ends of the film and the temperature in the widthwise middleportion of the film.

Next, the graphitized film was cooled to room temperature, andcompressed with a pressure of 10 MPa at room temperature.

Five films were produced in the same manner so that the number ofevaluations was n=5, and were evaluated for their sag reproducibility,sag Zgs, a-value, b-value, camber, resistance to tearing, and laminationproperty. As for the sag Zgs, a-value, b-value and camber, their maximumand minimum values of the five (n=5) evaluations are shown in Tables 5A,6A, 7A and 8A. The resistance to tearing and lamination property arealso shown in Tables 5A, 6A, 7A and 8A as “best evaluation value−worstevaluation value”. It should be noted that, in a case where the best andworst evaluations are the same, the result is shown as a singleevaluation value.

Comparative Example 2A

A graphite film was produced in the same manner as that described inExample 3A, except that a process similar to the sag controlling stepwas carried out in which the temperature at the entrance of the heattreatment apparatus was 655° C., the maximum temperature was 1400° C.,and the length of the furnace and the line speed were adjusted so thatthe temperature rise rate was 80° C. per minute (that is, thetemperature of the polymer film was suddenly raised from roomtemperature to 655° C., and therefore the sag controlling step was notcarried out). The various properties of the graphite film wereevaluated. The results are shown in Tables 5A, 6A, 7A and 8A.

Comparative Example 3A

The temperature at the entrance of the heat treatment apparatus waschanged to 300° C. (corresponding to the temperature at the start of thesag controlling step), the maximum temperature was changed to 400° C.,and the length of the furnace and the line speed were adjusted so thatthe temperature rise rate was 80° C. per minute (that is, a certaintemperature gradient along the widthwise direction of the film, whichwas given in the sag controlling step in Examples of the presentinvention, was given at a temperature lower than the startingtemperature of thermal decomposition). Next, the film was cooled to roomtemperature (23° C.), was wound into a roll having an inner diameter of100 mm, and was set in a carbonizing furnace so that the widthwisedirection of the film was parallel to the vertical direction (see FIG.16). The film was carbonized by heat treatment while raising thetemperature in the carbonizing furnace from room temperature to 1400° C.at 2° C. per minute without particular control of the temperatures atboth widthwise ends of the film and the temperature in a widthwisemiddle portion of the film.

Next, the carbonized film was cooled to room temperature, was set in agraphitization furnace in the same manner as in the carbonization, andwas graphitized by heat treatment while raising the temperature in thegraphitization furnace from room temperature (23° C.) to 2900° C. at0.5° C. per minute without particular control of the temperatures at theboth widthwise ends of the film and the temperature in the widthwisemiddle portion of the film.

Next, the graphitized film was cooled to room temperature, andcompressed with a pressure of 10 MPa at room temperature.

Five films were produced in the same manner so that the number ofevaluations was n=5, and were evaluated for their sag reproducibility,sag Zgs, a-value, b-value, camber, resistance to tearing, and laminationproperty. As for the sag Zgs, a-value, b-value and camber, their maximumand minimum values of the five (n=5) evaluations are shown in Tables 5A,6A, 7A and 8A. The resistance to tearing and lamination property arealso shown in Tables 5A, 6A, 7A and 8A as “best evaluation value−worstevaluation value”. It should be noted that, in a case where the best andworst evaluations are the same, the result is shown as a singleevaluation value.

Reference Example 1A

A graphite film was produced in the same manner as that described inExample 1A, except that the temperatures at both widthwise ends of apolymer film and the temperature in a widthwise middle portion of thepolymer film were the same. The various properties of the graphite filmwere evaluated. The results are shown in Tables 5A, 6A, 7A and 8A.

Reference Example 2A

A graphite film was produced in the same manner as that described inExample 1A, except that a linear temperature gradient along thewidthwise direction was such that each of the temperatures at bothwidthwise ends of a polymer film was 5° C. lower than the temperature ina middle portion of the polymer film. The various properties of thegraphite film were evaluated. The results are shown in Tables 5A, 6A, 7Aand 8A.

TABLE 5A Raw Material Film Thickness Width Length Type Birefringence μmmm m Comparative NPI 0.14 75 200 10 Example 1A Comparative NPI 0.14 75200 10 Example 2A Comparative NPI 0.14 75 200 10 Example 3A ReferenceNPI 0.14 75 200 10 Example 1A Reference NPI 0.14 75 200 10 Example 2A

TABLE 6A Sag Controlling Step Max Number of Starting Temp of Temp NumberMeasure- Temp Thermal Sag Temp in of ment Rise Decompositon ControllingTemp Gradient Heat Measure- Positions Pulling Rate End 1 Middle End 2End 1 Middle End 2 Max Mn Treat- ment Satisfying Strength Load ° C./Method ° C. ° C. ° C./m ment Positions Conditions kgf/cm2 g/cm2 minComparative Not Carried Out Example 1A Comparative CLFPM*1 660 655 6601405 1400 1405 25 25 1400 4 4 30 2 80 Example 2A Comparative CLFPM*1 305300 305 405 400 405 25 25 400 4 4 30 2 80 Example 3A Reference CLFPM*1500 500 500 580 580 580 0 0 580 4 4 30 2 80 Example 1A Reference CLFPM*1495 500 495 575 580 575 −25 −25 580 4 4 30 2 80 Example 2A *1CLFPMstands for “continuous long film processing method”.

TABLE 7A Physical Properties of Film After Sag Controlling Step CrackingCarbonization Step (Paper Widthwise Graphitization Step Tube WeightWeight Total Temp Temp Temp Wrap- Retention Loss Trans- Max DifferenceRise Max Rise around Rate Rate mittance Method of Temp of Film RateMethod of Temp Rate Test) % % % Setting ° C. ° C. ° C./min Setting ° C.° C./min Compression Comparative No Sag Controlling Step Cylindrical1400 0 2 Cylindrical 2900 0.5 Carried Example 1A Roll Roll OutComparative E 97.2 2.8 0.20 Cylindrical 1400 0 2 Cylindrical 2900 0.5Carried Example 2A Roll Roll Out Comparative E 97.2 2.8 0.20 Cylindrical1400 0 2 Cylindrical 2900 0.5 Carried Example 3A Roll Roll Out ReferenceA 97.2 2.8 0.20 Cylindrical 1400 0 2 Cylindrical 2900 0.5 CarriedExample 1A Roll Roll Out Reference A 97.2 2.8 0.20 Cylindrical 1400 0 2Cylindrical 2900 0.5 Carried Example 2A Roll Roll Out

TABLE 8A Physical Properties of Graphitized Film Sag Sag a-Value b-ValueCamber Repro- Max Mn Max Mn Max Mn Max Mn Resistance Laminationducibility mm mm mm mm to Tearing Property Comparative E 140 50 100 0 500 10 <2 A-E E Example 1A Comparative E 135 45 100 0 45 0 10 <2 A-E EExample 2A Comparative E 140 50 100 0 50 0 10 <2 A-E E Example 3AReference A 0 0 0 0 0 0 <2 <2 D A Example 1A Reference A 40 38 0 0 40 38<2 <2 E B Example 2A

<Sag Controlling Step>

A comparison was made between Examples 1A to 21A including the sagcontrolling step and Comparative Example 1A including no sag controllingstep. The graphite film of Comparative Example 1A including no sagcontrolling step had a poor sag reproducibility rated as “E” and hadvarying depths of sag. The resistance to tearing also greatly varied,and the worst evaluation value of the five (n=5) evaluations was “E”.The lamination property of each of the five samples was also very poorand rated as “E”. The graphite films of Examples 1A to 21A including thesag controlling step had improved resistance to tearing and laminationproperty.

<Temperature Gradient>

A comparison was made among Examples 1A to 5A, 18A and 21A and ReferenceExamples 1A and 2A, which had different temperature gradients. InExamples 1A to 5A in which a temperature gradient over an area extendingfrom the both widthwise ends of the polymer film toward the widthwisemiddle portion was not less than 2.5° C./m, the films had highresistance to tearing and good lamination property. In Example 3A inwhich a temperature gradient over an area extending from the bothwidthwise ends of the polymer film toward the widthwise middle portionwas 25° C./m, the film had a sag with an appropriate depth at bothwidthwise ends thereof and had very high resistance to tearing and verygood lamination property.

A comparison was made between Example 3A (in which the temperaturegradient on the left side was the same as the temperature gradient onthe right side) and Example 6A (in which the temperature gradient on theleft side was different from the temperature gradient on the rightside). It was found that the graphite film obtained in Example 6A hadcamber.

<Sag Controlling Temperature>

A comparison was made among Examples 3A and 7A to 10A which haddifferent sag controlling temperatures. Higher sag controllingtemperatures brought about deeper sags in both widthwise ends. Inparticular, the films obtained in Examples 3A, 8A, 9A and 10A had highresistance to tearing. Furthermore, the depth of sag was substantiallythe same between Example 10A and Examples 11A and 12A. This showed thatthe depth of sag would not change anymore after the sag controllingtemperature reached 655° C.

Furthermore, it was found that, in Examples 3A, 7A and 8A in which thesag controlling temperature was equal to or lower than 605° C., thefilms after the sag controlling step had less cracks and thus were easyto handle. Furthermore, it was found that, in Comparative Examples 2Aand 3A in which a process similar to the sag controlling step wascarried out outside a temperature range from the starting temperature ofthermal decomposition to the sag controlling temperature, the films hadpoor sag reproducibility as with Comparative Example 1A in which the sagcontrolling step was not carried out and sag was not controlled.

<Temperature Gradient in Each Measurement Position>

A comparison was made among Examples 3A, 19A and 20A. In all of theseexamples, in at least part of the temperature range from the startingtemperature of thermal decomposition of the polymer film to thetemperature at which the weight loss rate of the polymer film reached20.0%, (i) each of the temperatures at the both widthwise ends of thepolymer film was higher than the temperature in the widthwise middleportion of the polymer film and (ii) the temperature gradient over anarea extending from the both widthwise ends to the widthwise middleportion was equal to or greater than 2.5° C./m. Thus, in all of theseexamples, sag was controlled. Of these examples, Example 3A, which metthe above conditions in all of the temperature measuring positions inthe sag controlling step, best controlled sag.

Examples B According to Second Embodiment

The following description discusses conditions for the measurement ofvarious physical properties. In the following description, only thedifferences between Examples A according to the first embodiment andExamples B according to the second embodiment are discussed, and thosethat are the same between both examples are omitted. In Examples Baccording to the second embodiment, the maximum and minimum values offive (n=5) evaluations are shown in Tables.

<Evaluation of Cambering Property>

Evaluation of cambering property was carried out on the basis of thecamper measurement in accordance with JIS C2151. The cambering propertywas rated as: “A” when camper was 30 mm or greater; “B” when camper wasnot less than 20 mm and less than 30 mm; “C” when camper was not lessthan 15 mm and less than 20 mm; “D” when camper was not less than 11 mmand less than 15 mm; and “E” when camper was less than 11. The resultsare expressed as “best evaluation value−worst evaluation value”. In acase where the best and worst evaluations are the same, the result isshown as a single evaluation value.

<Evaluation of Rolling Property>

The rolling property of a graphite film was evaluated as illustrated inFIG. 22. More specifically, GS3 having a size of 200 mm in width×5 m wasrolled spread with the use of 2-ton Precision Roll Press (clearancedisplay system) available from Thank Metal Co., LTD. A lowerrolling-mill roll used here was a metallic roll made of SKD11 (having ahardness of greater than D95) having a size of 200 mm in diameter×250 mmin width, and an upper rolling-mill roll used here was an urethane rollhaving a hardness of D77 and a size of 200 mm in diameter×250 mm inwidth. The evaluation was carried out under the following condition: theclearance between the rolling-mill rolls was adjusted to −200 μm; atensile force of 30 g/cm was applied to the graphite film in the MDdirection; the graphite film was continuously supplied between the upperrolling-mill roll and the lower rolling-mill roll so that the angleformed by a line connecting (the starting point of contact between theupper rolling-mill roll and the graphite film) and (the center point ofthe upper rolling-mill roll) and a line connecting (the center point ofthe upper rolling-mill roll) and (the point of contact between the upperrolling-mill roll and the lower rolling-mill roll) was 120 degrees (FIG.22); and the line speed was 2 m per minute.

After the rolling property test, wrinkles as shown in FIG. 17 wereevaluated in the following manner. Across the whole area of the roll,wrinkles of not less than 5 mm in length were counted and converted asthe number of visible wrinkles across the width of the film per unitlongitudinal length (1 m). The graphite films were rated as: “A” whenthe number of wrinkles per meter was 0; “B” when the number of wrinklesper meter was greater than 0 and less than 0.05; “C” when the number ofwrinkles per meter was not less than 0.05 and less than 0.2; “D” whenthe number of wrinkles per meter was not less than 0.2 and less than 1;and “E” when the number of wrinkles per meter was not less than 1.

The results are expressed as “best evaluation value−worst evaluationvalue”. In a case where the best and worst evaluations are the same, theresult is shown as a single evaluation value.

<Evaluation of Lamination Property to Copper Foil Tape>

The graphite film was supplied between the first roll and the secondroll such that the angle formed by a line connecting (the starting pointof contact between the first roll and the graphite film) and (the centerpoint of the first roll) and a line connecting (the center point of thefirst roll) and (the point of contact between the first roll and thesecond roll) was 120 degrees (see FIG. 14). The PET tape was E-1100LCavailable from DIC. The PET tape was supplied to the second roll so thatthe angle formed by a line connecting (the starting point of contactbetween the second roll and the copper foil tape) and (the center pointof the second roll) and a line connecting (the center point of thesecond roll) and (the point of contact between the first roll and thesecond roll) was 120 degrees. A tensile force to be applied in the MDdirection of the graphite film was 30 g/cm, and the rewinding speed was1 m per minute.

Wrinkles (as shown in FIG. 21) of the graphite films after thecompletion of the laminating test were evaluated as follows. Across thewhole area of the roll, wrinkles of not less than 5 mm in length werecounted and converted as the number of visible wrinkles across the widthof the film per unit lengthwise length (1 m). The graphite compositefilms were rated as: “A” when the number of wrinkles per meter was 0;“B” when the number of wrinkles per meter was greater than 0 and lessthan 0.05; “C” when the number of wrinkles per meter was not less than0.05 and less than 0.2; “D” when the number of wrinkles per meter wasnot less than 0.2 and less than 1; and “E” when the number of wrinklesper meter was not less than 1.

The results are expressed as “best evaluation value−worst evaluationvalue”. In a case where the best and worst evaluations are the same, theresult is shown as a single evaluation value.

Example 1B

A polymer film used here was a polyimide film Apical NPI (available fromKaneka Corporation) having a birefringence of 0.14, thickness of 75 μm,width of 200 mm and length of 10 m. In Apical NPI, the temperaturescorresponding to the weight loss rates 1.0%, 1.1%, 2.8%, 10.0%, 15.0%and 20.0% in the measurement method of the present invention are 500°C., 520° C., 550° C., 580° C., 600° C., 630° C. and 655° C.,respectively. The polymer film was set to a rewinding apparatus asillustrated in FIG. 8, and the sag controlling step was carried outwhile the polymer film was continuously supplied to a heat treatmentapparatus. The length of the heat treatment apparatus along the MDdirection was 60 cm and the length along the TD direction was 30 cm. Thetemperature in a widthwise middle portion of the polymer film wascontrolled such that (i) the temperature at an entrance of the heattreatment apparatus was 500° C. (corresponding to the startingtemperature of thermal decomposition of the polymer film used in thepresent example), (ii) the temperature in a position 50 cm away from theentrance was the maximum temperature 580° C. (corresponding to the sagcontrolling temperature for the polymer film used in the presentexample), and (iii) the temperature at an exit, which is 10 cm away fromthe position of the maximum temperature, was 500° C. A lineartemperature gradient was given so that the widthwise middle portion ofthe polymer film had a temperature distribution along the lengthwisedirection of the polymer film as shown in FIG. 8. The line speed wascontrolled so that the actual temperature of the polymer film wouldincrease at 80° C. per minute (equivalent to a line speed of 50 cm perminute) in the 500° C.-580° C. range. Furthermore, a linear temperaturegradient was given also along the widthwise direction so that (i) thetemperature in the middle portion of the polymer film was 1° C. higherthan the temperatures at both widthwise ends (each of which is 10 cmaway from the widthwise middle portion) of the polymer film and (ii) thepolymer film had a temperature distribution along the widthwisedirection of the polymer film as shown in FIG. 8. The temperaturegradient along the widthwise direction was measured in four positions,i.e., the positions where the temperatures in the widthwise middleportion of the polymer film were 500° C., 530° C., 560° C. and 580° C.It was confirmed that, in each of the four positions, the temperature inthe widthwise middle portion was 1° C. higher than that at each of thewidthwise ends.

The polymer film was conveyed while a tensile force was applied to thefilm with a tensile strength of 30 kgf/cm². In the heat treatmentapparatus, the film was conveyed through a gap between graphite jigsplaced above and below the film (see FIG. 8). A pressure of 2 g/cm² wasapplied to the film in its thickness direction. After the sagcontrolling step, the film was evaluated for cracks and was measured forthe weight retention rate, weight loss rate and total transmittance.

Next, the film having been subjected to the sag controlling step wascooled to room temperature (23° C.), was wound into a roll having aninner diameter of 100 mm, and was set in a carbonizing furnace so thatthe widthwise direction of the film was parallel to the verticaldirection (see FIG. 16). The film was carbonized by heat treatment whileraising the temperature in the carbonizing furnace from room temperatureto 1400° C. at 2° C. per minute without particular control of thetemperatures at the both widthwise ends of the film and the temperaturein the widthwise middle portion of the film.

Next, the carbonized film was cooled to room temperature (23° C.), wasset in a graphitization furnace in the same manner as in thecarbonization, and was graphitized by heat treatment while raising thetemperature in the graphitization furnace from room temperature to 2900°C. at 0.5° C. per minute without particular control of the temperaturesat the both widthwise ends of the film and the temperature in thewidthwise middle portion of the film.

Next, the graphitized film was cooled to room temperature, andcompressed with a pressure of 10 MPa at room temperature.

Five films were produced in the same manner so that the number ofevaluations was n=5, and were evaluated for their sag reproducibility,sag Zgs, a-value, b-value, camber, rolling property, and laminationproperty to copper foil tape. As for the sag Zgs, a-value, b-value andcamber, the maximum and minimum values of the five (n=5) evaluations areshown in Table 4B. The rolling property, lamination property to copperfoil tape, and cambering property are also shown in Tables 1B, 2B, 3Band 4B as “best evaluation value−worst evaluation value”. It should benoted that, in a case where the best and worst evaluations are the same,the result is shown as a single evaluation value.

Example 2B

A graphite film was produced in the same manner as that described inExample 1B, except that a linear temperature gradient along thewidthwise direction was such that the temperature in the widthwisemiddle portion of a polymer film was 3° C. higher than each of thetemperatures at the both widthwise ends of the polymer film. The variousproperties of the graphite film were evaluated. The results are shown inTables 1B, 2B, 3B and 4B.

Example 3B

A graphite film was produced in the same manner as that described inExample 1B, except that a linear temperature gradient along thewidthwise direction was such that the temperature in the widthwisemiddle portion of a polymer film was 5° C. higher than each of thetemperatures at the both widthwise ends of the polymer film. The variousproperties of the graphite film were evaluated. The results are shown inTables 1B, 2B, 3B and 4B.

Example 4B

A graphite film was produced in the same manner as that described inExample 1B, except that a linear temperature gradient along thewidthwise direction was such that the temperature in the widthwisemiddle portion of a polymer film was 10° C. higher than each of thetemperatures at the both widthwise ends of the polymer film. The variousproperties of the graphite film were evaluated. The results are shown inTables 1B, 2B, 3B and 4B.

Example 5B

A graphite film was produced in the same manner as that described inExample 1B, except that a linear temperature gradient along thewidthwise direction was such that the temperature in the widthwisemiddle portion of a polymer film was 20° C. higher than each of thetemperatures at the both widthwise ends of the polymer film. The variousproperties of the graphite film were evaluated. The results are shown inTables 1B, 2B, 3B and 4B.

Example 6B

A graphite film was produced in the same manner as that described inExample 3B, except that, in the sag controlling step, the maximumtemperature in the heat treatment apparatus was 555° C. and the lengthof the furnace and the line speed were adjusted so that the temperaturerise rate was 80° C. per minute. The various properties of the graphitefilm were evaluated. The results are shown in Tables 1B, 2B, 3B and 4B.

Example 7B

A graphite film was produced in the same manner as that described inExample 3B, except that, in the sag controlling step, the maximumtemperature in the heat treatment apparatus was 605° C. and the lengthof the furnace and the line speed were adjusted so that the temperaturerise rate was 80° C. per minute. The various properties of the graphitefilm were evaluated. The results are shown in Tables 1B, 2B, 3B and 4B.

Example 8B

A graphite film was produced in the same manner as that described inExample 3B, except that, in the sag controlling step, the maximumtemperature in the heat treatment apparatus was 630° C. and the lengthof the furnace and the line speed were adjusted so that the temperaturerise rate was 80° C. per minute. The various properties of the graphitefilm were evaluated. The results are shown in Tables 1B, 2B, 3B and 4B.

Example 9B

A graphite film was produced in the same manner as that described inExample 3B, except that, in the sag controlling step, the maximumtemperature in the heat treatment apparatus was 655° C. and the lengthof the furnace and the line speed were adjusted so that the temperaturerise rate was 80° C. per minute. The various properties of the graphitefilm were evaluated. The results are shown in Tables 1B, 2B, 3B and 4B.

Example 10B

A graphite film was produced in the same manner as that described inExample 1B, except that a linear temperature gradient along thewidthwise direction was such that the temperature in the widthwisemiddle portion of a polymer film was 0.5° C. higher than each of thetemperatures at both widthwise ends of the polymer film. The variousproperties of the graphite film were evaluated. The results are shown inTables 1B, 2B, 3B and 4B.

Comparative Example 1B

A polymer film, which had not been subjected to the sag controllingstep, was carbonized in the following manner. The polymer film used herewas a polyimide film Apical NPI (available from Kaneka Corporation)having a birefringence of 0.14, thickness of 75 μm, width of 200 mm andlength of 10 m. In the same manner as in Example 1B, each film was woundinto a roll having an inner diameter of 100 mm, was set in a carbonizingfurnace so that the widthwise direction of the film was parallel to thevertical direction (see FIG. 16), and was carbonized by heat treatmentwhile raising the temperature in the carbonizing furnace from roomtemperature to 1400° C. at 2° C. per minute without particular controlof the temperatures at both widthwise ends of the film and thetemperature in a widthwise middle portion of the film.

Next, the carbonized film was cooled to room temperature (23° C.), wasset in a graphitization furnace in the same manner as in thecarbonization, and was graphitized by heat treatment while raising thetemperature in the graphitization furnace from room temperature to 2900°C. at 0.5° C. per minute without particular control of the temperaturesat the both widthwise ends of the film and the temperature in thewidthwise middle portion of the film.

Next, the graphitized film was cooled to room temperature (23° C.), andcompressed with a pressure of 10 MPa at room temperature.

Five films were produced in the same manner so that the number ofevaluations was n=5, and were evaluated for their sag reproducibility,sag Zgs, a-value, b-value, camber, rolling property, lamination propertyto copper foil tape, and cambering property. As for the sag Zgs,a-value, b-value and camber, the maximum and minimum values of the five(n=5) evaluations are shown in Table 4B. The rolling property,lamination property to copper foil tape, and cambering property are alsoshown in Tables 1B to 12B as “best evaluation value−worst evaluationvalue”. It should be noted that, in a case where the best and worstevaluations are the same, the result is shown as a single evaluationvalue.

Comparative Example 2B

A graphite film was produced in the same manner as that described inExample 3B, except that a process similar to the sag controlling stepwas carried out in the following condition: the temperature at theentrance of the heat treatment apparatus was 655° C., the maximumtemperature was 1400° C., and the length of the furnace and the linespeed were adjusted so that the temperature rise rate was 80° C. perminute (that is, the temperature of the polymer film was suddenly raisedfrom room temperature to 655° C., and therefore the sag controlling stepwas not carried out). The various properties of the graphite film wereevaluated. The results are shown in Tables 1B, 2B, 3B and 4B.

Comparative Example 3B

A process similar to the sag controlling step was carried out in thefollowing condition: the temperature at the entrance of the heattreatment apparatus was 300° C. (corresponding to the temperature at thestart of the sag controlling step), the maximum temperature was 400° C.,and the length of the furnace and the line speed were adjusted so thatthe temperature rise rate was 80° C. per minute (that is, a certaintemperature gradient along the widthwise direction of the film, whichwas given in the sag controlling step in Examples of the presentinvention, was given at a temperature lower than the startingtemperature of thermal decomposition).

Next, the film was cooled to room temperature (23° C.), was wound into aroll having an inner diameter of 100 mm, and was set in a carbonizingfurnace so that the widthwise direction of the film was parallel to thevertical direction (see FIG. 16). The film was carbonized by heattreatment while raising the temperature in the carbonizing furnace fromroom temperature to 1400° C. at 2° C. per minute without particularcontrol of the temperatures at the both widthwise ends of the film andthe temperature in the widthwise middle portion of the film.

Next, the carbonized film was cooled to room temperature, was set in agraphitization furnace in the same manner as in the carbonization, andwas graphitized by heat treatment while raising the temperature in thegraphitization furnace from room temperature (23° C.) to 2900° C. at0.5° C. per minute without particular control of the temperatures at theboth widthwise ends of the film and the temperature in the widthwisemiddle portion of the film.

Next, the graphitized film was cooled to room temperature, andcompressed with a pressure of 10 MPa at room temperature.

Five films were produced in the same manner so that the number ofevaluations was n=5, and were evaluated for their sag reproducibility,sag Zgs, a-value, b-value, camber, rolling property, lamination propertyto copper foil tape and cambering property. As for the sag Zgs, a-value,b-value and camber, the maximum and minimum values of the five (n=5)evaluations are shown in Table 4B. The rolling property, laminationproperty to copper foil tape, and cambering property are also shown inTables 1B, 2B, 3B and 4B as “best evaluation value−worst evaluationvalue”. It should be noted that, in a case where the best and worstevaluations are the same, the result is shown as a single evaluationvalue.

TABLE 1B Raw Material Film Thickness Width Length Type Birefringence μmmm m Example 1B NPI 0.14 75 200 10 Example 2B NPI 0.14 75 200 10 Example3B NPI 0.14 75 200 10 Example 4B NPI 0.14 75 200 10 Example 5B NPI 0.1475 200 10 Example 6B NPI 0.14 75 200 10 Example 7B NPI 0.14 75 200 10Example 8B NPI 0.14 75 200 10 Example 9B NPI 0.14 75 200 10 Example 10BNPI 0.14 75 200 10 Comparative NPI 0.14 75 200 10 Example 1B ComparativeNPI 0.14 75 200 10 Example 2B Comparative NPI 0.14 75 200 10 Example 3B

TABLE 2B Sag Controlling Step Temp Gradient Number between Max ofStarting Temp Each End Temp Number Measure- of Thermal Sag and Middle inof ment Temp Decomposition Controlling Temp Portion Heat Measure-Positions Pulling Rise End 1 Middle End 2 End 1 Middle End 2 Max MnTreat- ment Satisfying Strength Load Rate Method ° C. ° C. ° C./m mentPositions Conditions kgf/cm2 g/cm2 ° C./min Example 1B CLFPM*1 499 500499 579 580 579 −5 −5 580 4 4 30 2 80 Example 2B CLFPM*1 497 500 497 577580 577 −15 −15 580 4 4 30 2 80 Example 3B CLFPM*1 495 500 495 575 580575 −25 −25 580 4 4 30 2 80 Example 4B CLFPM*1 490 500 490 570 580 570−50 −50 580 4 4 30 2 80 Example 5B CLFPM*1 480 500 480 560 580 560 −100−100 580 4 4 30 2 80 Example 6B CLFPM*1 495 500 495 550 555 550 −25 −25555 3 3 30 2 80 Example 7B CLFPM*1 495 500 495 600 605 600 −25 −25 605 55 30 2 80 Example 8B CLFPM*1 495 500 495 625 630 625 −25 −25 630 6 6 302 80 Example 9B CLFPM*1 495 500 495 650 655 650 −25 −25 655 7 7 30 2 80Example 10B CLFPM*1 499.5 500 499.5 579.5 580 579.5 −2.5 −2.5 580 4 4 302 80 Comparative Not Carried Out Example 1B Comparative CLFPM*1 650 655650 1395 1400 1395 −25 −25 1400 4 4 30 2 80 Example 2B ComparativeCLFPM*1 295 300 295 395 400 395 −25 −25 400 4 4 30 2 80 Example 3B*1CLFPM stands for “continuous long film processing method”.

TABLE 3B Physical Properties of Film After Sag Controlling Step CrackingCarbonization Step (Paper Widthwise Graphitization Step Tube WeightWeight Total Temp Temp Temp Wrap- Retention Loss Trans- Max DifferenceRise Max Rise around Rate Rate mittance Method of Temp of Film RateMethod of Temp Rate Test) % % % Setting ° C. ° C. ° C./min Setting ° C.° C./min Example 1B A 97.2 2.8 0.20 Cylindrical Roll 1400 0 2Cylindrical Roll 2900 0.5 Example 2B A 97.2 2.8 0.20 Cylindrical Roll1400 0 2 Cylindrical Roll 2900 0.5 Example 3B A 97.2 2.8 0.20Cylindrical Roll 1400 0 2 Cylindrical Roll 2900 0.5 Example 4B A 97.22.8 0.20 Cylindrical Roll 1400 0 2 Cylindrical Roll 2900 0.5 Example 5BA 97.2 2.8 0.20 Cylindrical Roll 1400 0 2 Cylindrical Roll 2900 0.5Example 6B A 98.8 1.2 5.50 Cylindrical Roll 1400 0 2 Cylindrical Roll2900 0.5 Example 7B A 90.0 10.0 0.03 Cylindrical Roll 1400 0 2Cylindrical Roll 2900 0.5 Example 8B B 85.0 15.0 — Cylindrical Roll 14000 2 Cylindrical Roll 2900 0.5 Example 9B C 80.0 20.0 — Cylindrical Roll1400 0 2 Cylindrical Roll 2900 0.5 Example 10B A 97.2 2.8 0.20Cylindrical Roll 1400 0 2 Cylindrical Roll 2900 0.5 Comparative No SagControlling Step Cylindrical Roll 1400 0 2 Cylindrical Roll 2900 0.5Example 1B Comparative E 97.2 2.8 0.20 Cylindrical Roll 1400 0 2Cylindrical Roll 2900 0.5 Example 2B Comparative E 97.2 2.8 0.20Cylindrical Roll 1400 0 2 Cylindrical Roll 2900 0.5 Example 3B

TABLE 4B Physical Properties of Graphitized Film Evaluation Sag of Zgsa-Value b-Value Camber Evaluation Lamination Sag Max Mn Max Mn Max MnMax Mn of Rolling Property to Reproducibility mm mm mm mm PropertyCopper Foil Example 1B A 10 9 0 0 10 9 <2 <2 A B Example 2B A 30 28 0 030 28 <2 <2 A C Example 3B A 40 38 0 0 40 38 <2 <2 A D Example 4B A 7065 0 0 70 65 <2 <2 B E Example 5B A 90 85 0 0 90 85 <2 <2 B E Example 6BB 30 20 0 0 30 20 <2 <2 A C Example 7B A 45 43 0 0 45 43 <2 <2 A DExample 8B A 48 45 0 0 48 45 <2 <2 A D Example 9B A 50 48 0 0 50 48 <2<2 A D Example 10B A 5 5 0 0 5 5 <2 <2 B B Comparative E 140 50 100 0 500 10 <2 A-E E Example 1B Comparative E 135 45 100 0 45 0 10 <2 A-E EExample 2B Comparative E 140 50 100 0 50 0 10 <2 A-E E Example 3B

Example 11B

A graphite film was produced in the same manner as that described inExample 6B, except that, for the sag controlling temperature, (i) thetemperature at one widthwise end was the same as the temperature in thewidthwise middle portion and (ii) only the temperature at the otherwidthwise end was 0.2° C. higher than the temperature in the widthwisemiddle portion. The various properties of the graphite film wereevaluated. The results are shown in Tables 5B, 6B, 7B and 8B.

Example 12B

A graphite film as produced in the same manner as that described inExample 3B, except that, for the sag controlling temperature, (i) thetemperature at one widthwise end was the same as the temperature in thewidthwise middle portion and (ii) only the temperature at the otherwidthwise end was 0.4° C. higher than the temperature in the widthwisemiddle portion. The various properties of the graphite film wereevaluated. The results are shown in Tables 5B, 6B, 7B and 8B.

Example 13B

A graphite film as produced in the same manner as that described inExample 7B, except that the temperatures at the both widthwise ends ofthe polymer film were the same as the temperature in the widthwisemiddle portion of the polymer film. The various properties of thegraphite film were evaluated. The results are shown in Tables 5B, 6B, 7Band 8B.

Example 14B

A graphite film as produced in the same manner as that described inExample 8B, except that, for the sag controlling temperature, (i) thetemperature at one widthwise end was the same as the temperature in thewidthwise middle portion and (ii) only the temperature at the otherwidthwise end was 0.4° C. higher than the temperature in the widthwisemiddle portion. The various properties of the graphite film wereevaluated. The results are shown in Tables 5B, 6B, 7B and 8B.

Example 15B

A graphite film as produced in the same manner as that described inExample 9B, except that the temperatures at the both widthwise ends ofthe polymer film were the same as the temperature in the widthwisemiddle portion. The various properties of the graphite film wereevaluated. The results are shown in Tables 5B, 6B, 7B and 8B.

Comparative Example 4B

A graphite film as produced in the same manner as that described inComparative Example 2B, except that the temperatures at the bothwidthwise ends of the polymer film were the same as the temperature inthe widthwise middle portion of the polymer film. The various propertiesof the graphite film were evaluated. The results are shown in Tables 5B,6B, 7B and 8B.

Comparative Example 5B

A graphite film as produced in the same manner as that described inComparative Example 3B, except that the temperatures at the bothwidthwise ends of the polymer film were the same as the temperature inthe widthwise middle portion. The various properties of the graphitefilm were evaluated. The results are shown in Tables 5B, 6B, 7B and 8B.

TABLE 5B Raw Material Film Thickness Width Length Type Birefringence μmmm m Example 11B NPI 0.14 75 200 10 Example 12B NPI 0.14 75 200 10Example 13B NPI 0.14 75 200 10 Example 14B NPI 0.14 75 200 10 Example15B NPI 0.14 75 200 10 Comparative NPI 0.14 75 200 10 Example 1BComparative NPI 0.14 75 200 10 Example 4B Comparative NPI 0.14 75 200 10Example 5B

TABLE 6B Sag Controlling Step Temp Gradient Number between Max ofStarting Temp of Each End Temp Number Measure- Thermal and Middle in ofment Temp Decomposition Sag Controlling Temp Portion Heat Measure-Positions Pulling Rise End 1 Middle End 2 End 1 Middle End 2 Max MnTreat- ment Satisfying Strength Load Rate Method ° C. ° C. ° C./m mentPositions Conditions kgf/cm2 g/cm2 ° C./min Example 11B CLFPM*1 500.2500 500 555.2 555 555 1 1 555 3 3 30 2 80 Example 12B CLFPM*1 500.4 500500 580.4 580 580 2 2 580 4 4 30 2 80 Example 13B CLFPM*1 500 500 500605 605 605 0 0 605 5 5 30 2 80 Example 14B CLFPM*1 500.4 500 500 630.4630 630 2 2 630 6 6 30 2 80 Example 15B CLFPM*1 500 500 500 655 655 6550 0 655 7 7 30 2 80 Comparative Not Carried Out Example 1B ComparativeCLFPM*1 655 655 655 1400 1400 1400 0 0 1400 4 4 30 2 80 Example 4BComparative CLFPM*1 300 300 300 400 400 400 0 0 400 4 4 30 2 80 Example5B *1CLFPM stands for “continuous long film processing method”.

TABLE 7B Physical Properties of Film After Sag Controlling Step CrackingCarbonization Step (Paper Widthwise Graphitization Step Tube WeightWeight Total Temp Temp Temp Wrap- Retention Loss Trans- Max DifferenceRise Max Rise around Rate Rate mittance Method of Temp of Film RateMethod of Temp Rate Test) % % % Setting ° C. ° C. ° C./min Setting ° C.° C./min Example 11B A 98.8  1.2 5.50 Cylindrical Roll 1400 0 2Cylindrical Roll 2900 0.5 Example 12B A 97.2  2.8 0.20 Cylindrical Roll1400 0 2 Cylindrical Roll 2900 0.5 Example 13B A 90.0 10.0 0.03Cylindrical Roll 1400 0 2 Cylindrical Roll 2900 0.5 Example 14B B 85.015.0 — Cylindrical Roll 1400 0 2 Cylindrical Roll 2900 0.5 Example 15B C80.0 20.0 — Cylindrical Roll 1400 0 2 Cylindrical Roll 2900 0.5Comparative No Sag Controlling Step Cylindrical Roll 1400 0 2Cylindrical Roll 2900 0.5 Example 1B Comparative E 97.2  2.8 0.20Cylindrical Roll 1400 0 2 Cylindrical Roll 2900 0.5 Example 4BComparative E 97.2  2.8 0.20 Cylindrical Roll 1400 0 2 Cylindrical Roll2900 0.5 Example 5B

TABLE 8B Physical Properties of Graphitized Film Evaluation Sag of Zgsa-Value b-Value Camber Evaluation Lamination Sag Max Mn Max Mn Max MnMax Mn of Rolling Property to Reproducibility mm mm mm mm PropertyCopper Foil Example 11B B 4 3 4 3 0 0 <2 <2 C A Example 12B A 3 2 3 2 00 <2 <2 C A Example 13B A 2 2 2 2 0 0 <2 <2 C A Example 14B A 2 1 2 1 00 <2 <2 C A Example 15B A 1 1 1 1 0 0 <2 <2 C A Comparative E 140 50 1000 50 0 10 <2 A-E E Example 1B Comparative E 135 45 100 0 45 0 10 <2 A-EE Example 4B Comparative E 140 50 100 0 50 0 10 <2 A-E E Example 5B

Example 16B

A graphite film was produced in the same manner as that described inExample 1B, except that a linear temperature gradient along thewidthwise direction was such that a temperature B of a widthwise middleportion of the polymer film was 0.5° C. higher than a temperature C ofone widthwise end of the polymer film and a temperature A of the otherwidthwise end of the polymer film was 0.5° C. higher than thetemperature B of the widthwise middle portion. The various properties ofthe graphite film were evaluated. Further, a cambering property was alsoevaluated. The results are shown in Tables 9B, 10B, 11B, and 12B.

Example 17B

A graphite film was produced in the same manner as that described inExample 1B, except that a linear temperature gradient along thewidthwise direction was such that a temperature B of a widthwise middleportion of the polymer film was 1.5° C. higher than a temperature C ofone widthwise end of the polymer film and a temperature A of the otherwidthwise end of the polymer film was 1.5° C. higher than thetemperature B of the widthwise middle portion. The various properties ofthe graphite film were evaluated. Further, a cambering property was alsoevaluated. The results are shown in Tables 9B, 10B, 11B, and 12B.

Example 18B

A graphite film was produced in the same manner as that described inExample 1B, except that a linear temperature gradient along thewidthwise direction was such that a temperature B of a widthwise middleportion of the polymer film was 2.5° C. higher than a temperature C ofone widthwise end of the polymer film and a temperature A of the otherwidthwise end of the polymer film was 2.5° C. higher than thetemperature B of the widthwise middle portion. The various properties ofthe graphite film were evaluated. Further, a cambering property was alsoevaluated. The results are shown in Tables 9B, 10B, 11B, and 12B.

Example 19B

A graphite film was produced in the same manner as that described inExample 1B, except that a linear temperature gradient along thewidthwise direction was such that a temperature B of a widthwise middleportion of the polymer film was 5° C. higher than a temperature C of onewidthwise end of the polymer film and a temperature A of the otherwidthwise end of the polymer film was 5° C. higher than the temperatureB of the widthwise middle portion. The various properties of thegraphite film were evaluated. Further, a cambering property was alsoevaluated. The results are shown in Tables 9B, 10B, 11B, and 12B.

Example 20B

A graphite film was produced in the same manner as that described inExample 1B, except that a linear temperature gradient along thewidthwise direction was such that a temperature B of a widthwise middleportion of the polymer film was 10° C. higher than a temperature C ofone widthwise end of the polymer film and a temperature A of the otherwidthwise end of the polymer film was 10° C. higher than the temperatureB of the widthwise middle portion. The various properties of thegraphite film were evaluated. Further, a cambering property was alsoevaluated. The results are shown in Tables 9B, 10B, 11B, and 12B.

Example 21B

A graphite film was produced in the same manner as that described inExample 3B, except that in the sag controlling step, the maximumtemperature in a heat treatment apparatus was changed to 555° C., thelength of the furnace and the line speed were adjusted so that thetemperature rise rate was 80° C. per minute, and a linear temperaturegradient was given to a polymer film widthwise so that a temperature Bof a widthwise middle portion of the polymer film was 2.5° C. higherthan a temperature C of one widthwise end of the polymer film and atemperature A of the other widthwise end of the polymer film was 2.5° C.higher than the temperature B of the widthwise middle portion. Thevarious properties of the graphite film were evaluated. Further, acambering property was also evaluated. The results are shown in Tables9B, 10B, 11B, and 12B.

Example 22B

A graphite film was produced in the same manner as that described inExample 3B, except that in the sag controlling step, the maximumtemperature in a heat treatment apparatus was changed to 605° C., thelength of the furnace and the line speed were adjusted so that thetemperature rise rate was 80° C. per minute, and a linear temperaturegradient along the widthwise direction was such that a temperature B ofa widthwise middle portion of the polymer film was 2.5° C. higher than atemperature C of one widthwise end of the polymer film and a temperatureA of the other widthwise end of the polymer film was 2.5° C. higher thanthe temperature B of the widthwise middle portion. The variousproperties of the graphite film were evaluated. Further, a camberingproperty was also evaluated. The results are shown in Tables 9B, 10B,11B, and 12B.

Example 23B

A graphite film was produced in the same manner as that described inExample 3B, except that in the sag controlling step, the maximumtemperature in a heat treatment apparatus was changed to 630° C., thelength of the furnace and the line speed were adjusted so that thetemperature rise rate was 80° C. per minute, and a linear temperaturegradient along the widthwise direction was such that a temperature B ofa widthwise middle portion of the polymer film was 2.5° C. higher than atemperature C of one widthwise end of the polymer film and a temperatureA of the other widthwise end of the polymer film was 2.5° C. higher thanthe temperature B of the widthwise middle portion. The variousproperties of the graphite film were evaluated. Further, a camberingproperty was also evaluated. The results are shown in Tables 9B, 10B,11B, and 12B.

Example 24B

A graphite film was produced in the same manner as that described inExample 3B, except that in the sag controlling step, the maximumtemperature in a heat treatment apparatus was changed to 655° C., thelength of the furnace and the line speed were adjusted so that thetemperature rise rate was 80° C. per minute, and a linear temperaturegradient along the widthwise direction was such that a temperature B ofa widthwise middle portion of the polymer film was 2.5° C. higher than atemperature C of one widthwise end of the polymer film and a temperatureA of the other widthwise end of the polymer film was 2.5° C. higher thanthe temperature B of the widthwise middle portion. The variousproperties of the graphite film were evaluated. Further, a camberingproperty was also evaluated. The results are shown in Tables 9B, 10B,11B, and 12B.

Example 25B

A graphite film was produced in the same manner as that described inExample 1B, except that a linear temperature gradient along thewidthwise direction was such that a temperature B of a widthwise middleportion of the polymer film was 0.25° C. higher than a temperature C ofone widthwise end of the polymer film and a temperature A of the otherwidthwise end of the polymer film was 0.25° C. higher than thetemperature B of the widthwise middle portion. The various properties ofthe graphite film were evaluated. Further, a cambering property was alsoevaluated. The results are shown in Tables 9B, 10B, 11B, and 12B.

Comparative Example 6B

A graphite film was produced in the same manner as that described inComparative Example 2B, except that a linear temperature gradient alongthe widthwise direction was such that a temperature B of a widthwisemiddle portion of the polymer film was 2.5° C. higher than a temperatureC of one widthwise end of the polymer film and a temperature A of theother widthwise end of the polymer film was 2.5° C. higher than thetemperature B of the widthwise middle portion. The various properties ofthe graphite film were evaluated. Further, a cambering property was alsoevaluated. The results are shown in Tables 9B, 10B, 11B, and 12B.

Comparative Example 7B

A graphite film was produced in the same manner as that described inComparative Example 3B, except that a linear temperature gradient alongthe widthwise direction was such that a temperature B of a widthwisemiddle portion of the polymer film was 2.5° C. higher than a temperatureC of one widthwise end of the polymer film and a temperature A of theother widthwise end of the polymer film was 2.5° C. higher than thetemperature B of the widthwise middle portion. The various properties ofthe graphite film were evaluated. Further, a cambering property was alsoevaluated. The results are shown in Tables 9B, 10B, 11B, and 12B.

TABLE 9B Raw Material Film Thickness Width Length Type Birefringence μmmm m Example 16B NPI 0.14 75 200 10 Example 17B NPI 0.14 75 200 10Example 18B NPI 0.14 75 200 10 Example 19B NPI 0.14 75 200 10 Example20B NPI 0.14 75 200 10 Example 21B NPI 0.14 75 200 10 Example 22B NPI0.14 75 200 10 Example 23B NPI 0.14 75 200 10 Example 24B NPI 0.14 75200 10 Example 25B NPI 0.14 75 200 10 Comparative NPI 0.14 75 200 10Example 1B Comparative NPI 0.14 75 200 10 Example 6B Comparative NPI0.14 75 200 10 Example 7B

TABLE 10B Sag Controlling Step Temp Gradient Number Starting Tempbetween Max of of Thermal Temp A Temp Number Measure- Temp DecompositionSag Controlling Temp and in of ment Rise Temp Temp Temp Temp Temp TempTemp C Heat Measure- Positions Pulling Load Rate A B C A B C Max MnTreat- ment Satisfying Strength g/ ° C./ Method ° C. ° C. ° C./m mentPositions Conditions kgf/cm2 cm2 min Example CLFPM*1 500.5 500 499.5580.5 580 579.5 −5 −5 580 4 4 30 2 80 16B Example CLFPM*1 501.5 500498.5 581.5 580 578.5 −15 −15 580 4 4 30 2 80 17B Example CLFPM*1 502.5500 497.5 582.5 580 577.5 −25 −25 580 4 4 30 2 80 18B Example CLFPM*1505 500 495 585 580 575 −50 −50 580 4 4 30 2 80 19B Example CLFPM*1 510500 490 590 580 570 −100 −100 580 4 4 30 2 80 20B Example CLFPM*1 502.5500 497.5 557.5 555 552.5 −25 −25 555 3 3 30 2 80 21B Example CLFPM*1502.5 500 497.5 607.5 605 602.5 −25 −25 605 5 5 30 2 80 22B ExampleCLFPM*1 502.5 500 497.5 632.5 630 627.5 −25 −25 630 6 6 30 2 80 23BExample CLFPM*1 502.5 500 497.5 657.5 655 652.5 −25 −25 655 7 7 30 2 8024B Example CLFPM*1 500.25 500 499.75 580.25 580 579.75 −2.5 −2.5 580 44 30 2 80 25B Compar- Not Carried Out ative Example 1B Compar- CLFPM*1657.5 655 652.5 1402.5 1400 1397.5 −25 −25 1400 4 4 30 2 80 ativeExample 6B Compar- CLFPM*1 302.5 300 297.5 402.5 400 397.5 −25 −25 400 44 30 2 80 ative Example 7B *1CLFPM stands for “continuous long filmprocessing method”.

TABLE 11B Physical Properties of Film After Sag Controlling StepCracking Carbonization Step (Paper Widthwise Graphitization Step TubeWeight Weight Total Temp Temp Temp Wrap- Retention Loss Trans- MaxDifference Rise Max Rise around Rate Rate mittance Method of Temp ofFilm Rate Method of Temp Rate Test) % % % Setting ° C. ° C. ° C./minSetting ° C. ° C./min Example 16B A 97.2 2.8 0.20 Cylindrical Roll 14000 2 Cylindrical Roll 2900 0.5 Example 17B A 97.2 2.8 0.20 CylindricalRoll 1400 0 2 Cylindrical Roll 2900 0.5 Example 18B A 97.2 2.8 0.20Cylindrical Roll 1400 0 2 Cylindrical Roll 2900 0.5 Example 19B A 97.22.8 0.20 Cylindrical Roll 1400 0 2 Cylindrical Roll 2900 0.5 Example 20BA 97.2 2.8 0.20 Cylindrical Roll 1400 0 2 Cylindrical Roll 2900 0.5Example 21B A 98.8 1.2 5.50 Cylindrical Roll 1400 0 2 Cylindrical Roll2900 0.5 Example 22B A 90.0 10.0 0.03 Cylindrical Roll 1400 0 2Cylindrical Roll 2900 0.5 Example 23B B 85.0 15.0 — Cylindrical Roll1400 0 2 Cylindrical Roll 2900 0.5 Example 24B C 80.0 20.0 — CylindricalRoll 1400 0 2 Cylindrical Roll 2900 0.5 Example 25B A 97.2 2.8 0.20Cylindrical Roll 1400 0 2 Cylindrical Roll 2900 0.5 Comparative No SagControlling Step Cylindrical Roll 1400 0 2 Cylindrical Roll 2900 0.5Example 1B Comparative E 97.2 2.8 0.20 Cylindrical Roll 1400 0 2Cylindrical Roll 2900 0.5 Example 6B Comparative E 97.2 2.8 0.20Cylindrical Roll 1400 0 2 Cylindrical Roll 2900 0.5 Example 7B

TABLE 12B Physical Properties of Graphitized Film Sag of Sag ofEvaluation Sag End at End at of Evaluation Zgs Temp A Temp C b-ValueCamber Evaluation Lamination of Sag Max Mn Max Mn Max Mn Max Mn Max Mnof Rolling Property to Cambering Reproducibility mm mm mm mm mm PropertyCopper Foil Property Example 16B A 10 9 10 9 0 0 5 5 14 13 C C C Example17B A 30 28 30 28 0 0 15 15 16 14 D D C Example 18B A 40 38 40 38 0 0 2020 20 19 E E B Example 19B A 70 65 70 65 0 0 35 34 30 28 E E A Example20B A 90 85 90 85 0 0 45 45 40 35 E E A Example 21B B 30 20 30 20 0 0 109 18 14 D D B Example 22B A 45 43 45 43 0 0 21 21 23 22 E E A Example23B A 48 45 48 45 0 0 23 23 25 24 E E A Example 24B A 50 48 50 48 0 0 2423 27 26 E E A Example 25B A 5 5 5 5 0 0 2 2 11 11 C C D Comparative E140 50 100 0 100 0 50 0 10 <2 A-E E C-E Example 1B Comparative E 135 45100 0 100 0 45 0 10 <2 A-E E C-E Example 6B Comparative E 140 50 100 0100 0 50 0 10 <2 A-E E C-E Example 7B

<Sag Controlling Step>

A comparison was made between Examples 1B through 25B including the sagcontrolling step and Comparative Example 1B including no sag controllingstep. The graphite film of Comparative Example 1B including no sagcontrolling step had a poor sag reproducibility rated as “E” and hadvarying depths of sag. The graphite film of Comparative Example 1B alsohad a poor lamination property to copper foil tape, which was also ratedas “E”. Further, in regard to each of the rolling property and thecambering property, the worst evaluation value of the five (n=5)evaluations was also E.

On the other hand, the graphite films of Examples 1B through 25Bincluding the sag controlling step each had the sag reproducibilityrated as “A” or “B”. As is clear from this, the sag was controlled inExamples 1B through 25B.

<Sag Controlling Temperature>

1) Regarding Graphite Films Having Sag in Middle Portion

A comparison was made among Examples 3B, and 6B through 9B havingrespectively different sag controlling temperature conditions. Thehigher the sag controlling temperature, the deeper the sag in thewidthwise middle portion.

In Comparative Examples 2B and 3B in which a treatment similar to thatin the sag controlling step was carried out at a temperature outside thetemperature range from the starting temperature of thermal decompositionto the sag controlling temperature, the graphite films each had a poorsag reproducibility as in Comparative Example 1B including no sagcontrolling step. As is clear from this, the sag was not controlled inComparative Examples 2B and 3B.

2) Flat Graphite Film Having No Sag

A comparison was made among Examples 11B through 15B having respectivelydifferent sag controlling temperature conditions. The higher the sagcontrolling temperature became, the flatter a graphite film obtainedwas.

In Comparative Examples 4B and 5B in which a treatment similar to thatin the sag controlling step was carried out at a temperature outside thetemperature range from the starting temperature of thermal decompositionto the sag controlling temperature, the graphite films each had a poorsag reproducibility as in Comparative Example 1B including no sagcontrolling step. As is clear from this, the sag was not controlled inComparative Examples 4B and 5B.

3) Graphite Film Having Sag at One Widthwise End

A comparison was made among Examples 18B, and 21B through 24B havingrespectively different sag control temperature conditions. The higherthe sag controlling temperature became, the deeper the sag of a graphitefilm obtained at one widthwise end was.

In Comparative Examples 6B and 7B in which a treatment similar to thatin the sag controlling step was carried out at a temperature outside thetemperature range from the starting temperature of thermal decompositionto the sag controlling temperature, the graphite films each had a poorsag reproducibility as in Comparative Example 1B including no sagcontrolling step. As is clear from this, the sag was not controlled inComparative Examples 6B and 7B.

<Temperature Gradient>

1) Regarding Graphite Films Having Sag in Middle Portion

A comparison was made among Examples 1B through 5B and 10B havingrespectively different sag controlling temperature conditions. InExamples 1B through 5B and 10B in which a temperature gradient over anarea extending from both widthwise ends toward the widthwise middleportion was not more than −2.5° C./m, all the graphite films had sag inthe widthwise middle portion. The smaller the temperature gradientbecame, the deeper the sag became.

3) Graphite Film Having Sag at One Widthwise End

A comparison was made among Examples 16B through 20B and 25B havingrespectively different sag controlling temperature conditions. InExamples 16B through 20B and 25B having a temperature gradient of notless than 2.5° C./m from the temperature A to the temperature C, all thegraphite films had sag in the widthwise middle portion. The larger thetemperature gradient became, the deeper the sag became.

Example 26B

A graphite film was produced in the same manner as that described inExample 1B, except that Apical AH manufactured by Kaneka Corporation,having a birefringence of 0.10, a thickness of 75 μm, a width of 200 mm,and a length of 10 m was employed as a polymer film. The variousproperties of the graphite film were evaluated. Table 13B shows thepolymer film (raw material film) employed in Example 26B and Tables 14B,15B and 16B show steps, results, etc.

Example 27B

A graphite film was produced in the same manner as that described inExample 1B, except that Kapton H manufactured by Du Pont-Toray Co.,Ltd., having a birefringence of 0.12, a thickness of 75 μm, a width of200 mm, and a length of 10 m was employed as a polymer film. The variousproperties of the graphite film were evaluated. Table 13B shows thepolymer film (raw material film) employed in Example 27B and Tables 14B,15B and 16B show steps, results, etc.

Example 28B

A graphite film was produced in the same manner as that described inExample 1B, except that POD (polyparaphenylene oxadiazole) having abirefringence of 0.12, a thickness of 75 μm, a width of 200 mm, and alength of 10 m was employed as a polymer film. The various properties ofthe graphite film were evaluated. Table 13B shows the polymer film (rawmaterial film) employed in Example 28B and Tables 14B, 15B and 16B showsteps, results, etc.

Example 28B showed that the sag control technique of the presentinvention can be applied to a polymer other than a polyimide filmwithout any problem.

Example 29B

A graphite film was produced in the same manner as that described inExample 1B, except that Apical NPI, which is a polyimide filmmanufactured by Kaneka Corporation, having a thickness of 50 μm wasemployed as a polymer film. The various properties of the graphite filmwere evaluated. Table 13B shows the polymer film (raw material film)employed in Example 29B and Tables 14B, 15B and 16B show steps, results,etc.

Example 30B

A graphite film was produced in the same manner as that described inExample 1B, except that Apical NPI, that is a polyimide filmmanufactured by Kaneka Corporation, having a thickness of 125 μm wasemployed as a polymer film. The various properties of the graphite filmwere evaluated. Table 13B shows the polymer film (raw material film)employed in Example 30B and Tables 14B, 15B and 16B show steps, results,etc.

The above results showed that the smaller the thickness of the polymerfilm becomes, the shallower the sag becomes, and that sagreproducibility is improved. The above results also showed that when thethickness of the polymer film is in a range of 50 μm to 125 μm, the sagtechnique of the present invention can be applied without any problem.

Example 31B

A graphite film was produced in the same manner as that described inExample 1B, except that Apical NPI, which is a polyimide filmmanufactured by Kaneka Corporation, having a width of 50 mm was employedas a polymer film. The various properties of the graphite film wereevaluated. Table 13B shows the polymer film (raw material film) employedin Example 31B and Tables 14B, 15B and 16B show steps, results, etc.

Example 32B

A graphite film was produced in the same manner as that described inExample 1B, except that Apical NPI, which is a polyimide filmmanufactured by Kaneka Corporation, having a width of 300 mm wasemployed as a polymer film. The various properties of the graphite filmwere evaluated. Table 13B shows the polymer film (raw material film)employed in Example 32B and Tables 14B, 15B and 16B show steps, results,etc.

The above results showed that a smaller width results in a shallowersag. The above results also showed that when the polymer film has awidth in a range of 50 mm to 300 mm, the sag control technique can beapplied without any problem.

Example 33B

A graphite film was produced in the same manner as that described inExample 1B, except that the carbonization step was omitted. The variousproperties of the graphite film were evaluated. Table 13B shows thepolymer film (raw material film) employed in Example 33B and Tables 14B,15B and 16B show steps, results, etc.

The results showed that even in a case where the carbonization step isnot carried out, the sag control technique of the present invention canbe applied without any problem.

Note that though Examples 26B through 33B above are based on thetechnique according to the second embodiment of the present invention,the same applies to other sag control technique according to the firstembodiment of the present invention in regard to a point that thepolymer film is not limited to a polyimide film, a thickness of thepolymer film, a width of the polymer film, and the presence/absence ofthe carbonization step.

TABLE 13B Raw Material Film Thick- ness Width Length Type Birefringenceμm mm m Example 26B AH 0.10 75 200 10 Example 27B KAPTON 0.12 75 200 10H Example 28B POD 0.90 75 200 10 Example 29B NPI 0.14 50 200 10 Example30B NPI 0.14 125 200 10 Example 31B NPI 0.14 75  50 10 Example 32B NPI0.14 75 300 10 Example 33B NPI 0.14 75 200 10

TABLE 14B Sag Controlling Step Temp Gradient between Number of SartingTemp of Each End Max Number Measure- Thermal Sag and Middle Temp of mentTemp Decomposition Controlling Temp Portion in Measure- PositionsPulling Rise End 1 Middle End 2 End 1 Middle End 2 Max Mn Heat mentSatisfying Strength Load Rate ° C. ° C. ° C./m Treatment Positionconditions kgf/cm2 g/cm2 ° C./min Example 26B CLFPM*1 495 500 495 575580 575 −25 −25 580 4 4 30 2 80 Example 27B CLFPM*1 495 500 495 575 580575 −25 −25 580 4 4 30 2 80 Example 28B CLFPM*1 495 500 495 575 580 575−25 −25 580 4 4 30 2 80 Example 29B CLFPM*1 495 500 495 575 580 575 −25−25 580 4 4 30 2 80 Example 30B CLFPM*1 495 500 495 575 580 575 −25 −25580 4 4 30 2 80 Example 31B CLFPM*1 495 500 495 575 580 575 −25 −25 5804 4 30 2 80 Example 32B CLFPM*1 495 500 495 575 580 575 −25 −25 580 4 430 2 80 Example 33B CLFPM*1 495 500 495 575 580 575 −25 −25 580 4 4 30 280 *1CLFPM stands for “continuous long film processing method”.

TABLE 15B Physical Properties of Film After Sag Controlling StepCracking Carbonization Step (Paper Widthwise Graphitization Step TubeWeight Weight Total Temp Temp Temp Wrap- Retention Loss Trans- MaxDifference Rise Max Rise around Rate Rate mittance Method of Temp ofFilm Rate Method of Temp Rate Test) % % % Setting ° C. ° C. ° C./minSetting ° C. ° C./min Example 26B A 97.2 2.8 0.20 Cylindrical Roll 14000 2 Cylindrical Roll 2900 0.5 Example 27B A 97.0 3.0 0.20 CylindricalRoll 1400 0 2 Cylindrical Roll 2900 0.5 Example 28B A 95.2 4.8 0.20Cylindrical Roll 1400 0 2 Cylindrical Roll 2900 0.5 Example 29B A 97.22.8 0.20 Cylindrical Roll 1400 0 2 Cylindrical Roll 2900 0.5 Example 30BA 97.2 2.8 0.20 Cylindrical Roll 1400 0 2 Cylindrical Roll 2900 0.5Example 31B A 97.2 2.8 0.20 Cylindrical Roll 1400 0 2 Cylindrical Roll2900 0.5 Example 32B A 97.2 2.8 0.20 Cylindrical Roll 1400 0 2Cylindrical Roll 2900 0.5 Example 33B A 97.2 2.8 0.20 Not Carried OutCylindrical Roll 2900 0.5

TABLE 16B Physical Properties of Graphitized Film Evaluation Sag of Zgsa-Value b-Value Camber Evaluation Lamination Sag Max Mn Max Mn Max MnMax Mn of Rolling Property to Reproducibility mm mm mm mm PropertyCopper Foil Example 26B A 42 38 0 0 42 38 <2 <2 A D Example 27B A 42 370 0 42 37 <2 <2 A D Example 28B A 45 36 0 0 45 36 <2 <2 A D Example 29BA 38 37 0 0 38 37 <2 <2 A D Example 30B A 41 34 0 0 41 34 <2 <2 A DExample 31B A 20 19 0 0 20 19 <2 <2 A B Example 32B A 60 55 0 0 60 55 <2<2 B D Example 33B A 40 32 0 0 40 32 <2 <2 A D

Examples C According to Third Embodiment

The following discusses conditions for measuring various physicalproperties in Examples C. Here, discussion of the conditions identicalto those of Examples A according to the first embodiment and Examples Baccording to the second embodiment discussed above are omitted, and onlyconditions different from those of Examples A and B are discussed.

<Conditions for Measuring Various Physical Properties>

<Sag Measurement (as Specified by JIS C2151) of Raw Graphite Film andGraphite Film)>

Flatness of a raw graphite film and a graphite film was evaluated by sagmeasurement in accordance with film windability evaluation as specifiedby JIS C2151. A depth of sag was measured at a room temperature (23°C.).

(Test Piece) A fresh test piece having a length of approximately 2 mdrawn from a roll is employed. In this process, the test piece is takenfrom around the center of a wound roll of film. More specifically, inthe case of a roll of 100 m, three test pieces are taken from around 50m away from the roll end. A sheet sample such as a sheet sample inExample 14C, from which three test pieces cannot be taken, is directlyemployed as a test piece and measurement is carried out only once.(Apparatuses) The following describes apparatuses employed in Examples C(FIG. 31).

a) Mount Equipped with Rolls

A basic arrangement is the same as the one described above andillustrated in FIG. 2, and the explanation thereof is omitted. However,an arrangement here is different from the one illustrated in FIG. 2, inthat a device (detachable shaft), like the one labeled 296 in FIG. 31,for placing a film roll to be tested is attached to the mount. Aposition where the device is attached to the mount is right below oneroll (first roll). This device is arranged such that 1) the detachableshaft on which the film is placed is in parallel to the axis of thefirst roll within 1 degree and 2) a position of a lateral part of thefilm can be freely adjusted.

b) Device for Applying Tensile Force to Film

A basic arrangement is the same as the one described above andillustrated in FIG. 2 and the explanation thereof is omitted.

c) Tools for Measuring Dimension

A basic arrangement is the same as the one described above andillustrated in FIG. 2 and the explanation thereof is omitted.

(Measurement Procedure) A basic procedure is the same as that ofExamples A described above.

(Results) The deepest sag value for each test piece was defined as sagZgs, and a median of three measured values was taken. For a sheetsample, a result of one measurement was put in Tables 1C and 2C.

<Measurement of Thermal Diffusivity of Raw Graphite Film and GraphiteFilm in Direction Parallel to Film Surface>

A thermal diffusivity of the raw graphite film and the graphite film ina direction parallel to each film surface was measured by using an ACcalorimeter Method Thermal Constant Analyzer (“LaserPIT” manufactured byULVAC-RIKO, Inc.). In this measurement, each sample prepared by cuttinga 4 mm×40 mm piece from the graphite film was measured at 10 Hz in anatmosphere of 23° C. From each of the raw graphite film and the graphitefilm, three test pieces were taken from points 1, 2, and 3 in FIG. 33.The point 1 is located at a position around the middle of each of theraw graphite film and the graphite film and 50 mm away from a roll startof each of the films. The point 3 is located at a position around themiddle of each of the raw graphite film and the graphite film and 50 mmaway from a roll end of each of the films. The point 2 is located at amidpoint between the points 1 and 3. In the case of a roll having a TDwidth of 200 mm, the term “the position around the middle” refers to aposition around 100 mm away from respective widthwise side edges. Notethat three test pieces were similarly cut from a sheet sample. Tables 1Cand 2C show an average value of thermal diffusivities measured by use ofthe three test pieces.

<Evaluation of Lamination Property to Copper Foil Tape>

The laminating test as illustrated in FIG. 34 was carried out. Morespecifically, a graphite film wrapped around a 3-in. diameter paper tubewas continuously supplied between a first roll and a second roll, whichwere provided in parallel with each other, each measuring 50 mm inexternal diameter and 635 mm in length, so that the graphite film waslaminated to a copper foil tape measuring 10 μm in thickness and 430 mmin width. In this process, the graphite film was supplied such that anangle formed by a line connecting (the starting point of contact betweenthe first roll and the graphite film) and (the center point of the firstroll) and a line connecting (the center point of the first roll) and(the point of contact between the first roll and the second roll) was120 degrees. The copper foil tape employed here was E-1100LCmanufactured by DIC. This copper foil tape was supplied such that anangle formed by a line connecting (the starting point of contact betweenthe second roll and the copper foil tape) and (the center point of thesecond roll) and a line connecting (the center point of the second roll)and (the point of contact between the first roll and the second roll)was 120 degrees. A tensile force to be applied in the MD direction ofthe graphite film was 30 g/cm, and the rewinding speed was 1 m perminute.

Wrinkles (as shown in FIG. 24) of the graphite films after thecompletion of the laminating test were evaluated as follows. Across thewhole area of the roll, wrinkles of not less than 5 mm in length werecounted and converted as the number of visible wrinkles across the widthof the film (a width of the graphite film is 450 mm in the presentExamples C, Comparative Examples C, and Reference Example C) per unitlengthwise length (1 m). The graphite composite films were rated as: “A”when the number of visible wrinkles across the width of the film permeter was 0; “B” when the number of visible wrinkles across the width ofthe film per meter was more than 0 and less than 0.05; “C” when thenumber of visible wrinkles across the width of the film per meter wasnot less than 0.05 and less than 0.2; “D” when the number of visiblewrinkles across the width of the film per meter was not less than 0.2and less than 1; and “E” when the number of visible wrinkles across thewidth of the film per meter was not less than 1.

<MIT Folding Endurance Test of Raw Graphite Film and Graphite Film>

A MIT folding endurance test of the raw graphite film and the graphitefilm was carried out. First, three test pieces of each of the films,having a size of 1.5 cm×10 cm, were cut from the points 1, 2, and 3 ofFIG. 33. Then, the MIT folding endurance test was carried out by usingMIT Type Folding Endurance Tester (Type D) manufactured by Toyo SeikiSeisaku-sho, Ltd. under the following conditions: a test load of 100 gf(0.98 N), a rate of 90 times per minute, and a folding clamp curvatureradius (R) of 2 mm. In an atmosphere at 23° C., each of the test pieceswas folded to the right and the left both at an angle of 135 degrees.The number of times of folding until the test piece was broken away wasmeasured. As a result of measurement of the three test pieces, anaverage value was shown in Tables 1C and 2C.

<Method for Producing Polyimide Film A>

To a DMF (dimethylformamide) solution dissolving 1 equivalent of4,4′-oxydianiline, 1 equivalent of pyromellitic dianhydride wasdissolved to give a polyamic acid solution (18.5% by weight). While thissolution was being cooled, 1 equivalent of acetic anhydride, 1equivalent of isoquinoline, and an imidization catalyst including DMFrelative to carboxylic acid groups included in the polyamic acid wereadded, and then the mixture was degassed.

The polyamic acid DMF solution prepared in the polymerization step wasmixed with a curing agent (acetic anhydride and isoquinoline) in a givenratio by using a blender, and a resulting mixture was continuously flownfrom a T-die and applied onto an endless belt. Then, thus appliedresulting mixture was dried up by hot air while the belt was rotated.When the above mixture varnish was heated, dehydration occurred in itsmolecules, and imidization reaction proceeded. A self-supporting film(gel film) having a remaining solvent ratio of approximately 46% at anexit of a belt chamber as a result of evaporation of the solvent wasstripped from the belt, and fixed in a pin frame. The film was subjectedto heat treatment for 4 minutes in total at temperatures in the rangefrom 300° C. to 580° C. in a tenter chamber. Thereby, a polyamide film Ahaving a thickness of 50 μm was produced. In the present study, apolyimide film (Product Name: Apical 200AV) manufactured by KanekaCorporation was employed.

Example 1C

The polyimide film A having a thickness of 50 μm, a width of 500 mm, anda length of 50 m was wrapped around a cylindrical graphite inner corehaving an external diameter of 100 mm and a length of 550 mm asillustrated in FIG. 29, and then covered with an external cylinderhaving an inner diameter of 130 mm. This cylinder container wastransversely set in an electric furnace. Then, the carbonization stepwas carried out under a condition where the temperature was raised by 2°C. per minute up to 1400° C.

Next, as shown in FIG. 30, thus obtained carbonized film in the form ofa roll was set to an internal core having an external diameter of 100 mmand transversely in a graphitization furnace (at this time, the internalcore is floated by an anchorage). The graphitization step was carriedout under a condition where the temperature was raised by 5° C. perminute up to 2900° C. Then, the temperature was decreased to a roomtemperature. After the graphitization step, various physical propertiesof a raw graphite film were measured. Thus measured physical propertieswere shown in Tables 1C and 2C. Note that the graphite film that has notundergone the straightening process after the graphitization step iscalled a “raw graphite film”.

The raw graphite film had a sag Zgs of 120 mm, a length of 45.0 m, and awidth of 450 mm.

Then, thus obtained raw graphite was fixed to an inner core 1 by bondingwith a double-faced tape produced by using a graphitized material(product number: MSG, linear expansion coefficient: 4.0×10⁻⁶/K)available from SEC Carbon, Ltd., and then wound around the inner core 1kept standing as illustrated in FIG. 28 so that a resultant roll had aleveled edge. The inner core 1 had a center circumference of 314.0000 mmand an end 1 circumference of 314.1338 mm, and an end 2 circumference of314.1338 mm (the center circumference of the inner core 1 had a minimumvalue and the circumference of the inner core 1 gradually increased fromthe center circumference to the end 1 circumference and the end 2circumference). Thereafter, while the outermost circumferential film ofthe raw graphite film was fixed not to move, the raw graphite film wastightened around the inner core by giving a torque of 4 N·m to a driveshaft. The rewinding step was carried out as described above.

Then, the raw graphite film tightened around the inner core wastransversely placed and set in the graphitization furnace and thestraightening-for-flatness process step was carried out under thecondition where a temperature was raised by 5° C. per minute up to 2900°C. As a result, a graphite film thus obtained had a sag Zgs of 20.0 mm,a length of 45.0 m, and a width of 450 mm. Then, various physicalproperties of the graphite film were measured. The results of thismeasurement are shown in Tables 1C and 2C.

Example 2C

A graphite film was produced in the same manner as that described inExample 1C, except that the inner core 1 employed in Example 2C had acenter circumference of 314.0000 mm and an end 1 circumference of314.0336 mm, and an end 2 circumference of 314.0336 mm (the centercircumference of the inner core 1 had a minimum value and thecircumference of the inner core 1 gradually increased from the centercircumference to the end 1 circumference and the end 2 circumference).As a result, thus obtained graphite film had a sag Zgs of 10.0 mm, alength of 45.0 m, and a width of 450 mm. Then, various physicalproperties of the graphite film were measured. The results of thismeasurement are shown in Tables 1C and 2C.

Example 3C

A graphite film was produced in the same manner as that described inExample 1C, except that the inner core 1 employed in Example 3C had acenter circumference of 314.0000 mm and an end 1 circumference of314.0085 mm, and an end 2 circumference of 314.0085 mm (the centercircumference of the inner core 1 had a minimum value and thecircumference of the inner core 1 gradually increased from the centercircumference to the end 1 circumference and the end 2 circumference).As a result, thus obtained graphite film had a sag Zgs of 5.0 mm, alength of 45.0 m, and a width of 450 mm. Then, various physicalproperties of the graphite film were measured. The results of thismeasurement are shown in Tables 1C and 2C.

Example 4C

A graphite film was produced in the same manner as that described inExample 1C, except that the inner core 1 employed in Example 4C had acenter circumference of 314.0000 mm and an end 1 circumference of314.0019 mm, and an end 2 circumference of 314.0019 mm (the centercircumference of the inner core 1 had a minimum value and thecircumference of the inner core 1 gradually increased from the centercircumference to the end 1 circumference and the end 2 circumference).As a result, thus obtained graphite film had a sag Zgs of 1.0 mm, alength of 45.0 m, and a width of 450 mm. Then, various physicalproperties of the graphite film were measured. The results of thismeasurement are shown in Tables 1C and 2C.

Example 5C

A graphite film was produced in the same manner as that described inExample 1C, except that the inner core 1 employed in Example 5C had acenter circumference of 314.0000 mm and an end 1 circumference of314.0000 mm, and an end 2 circumference of 314.0000 mm. As a result,thus obtained graphite film had a sag Zgs of 0.1 mm, a length of 45.0 m,and a width of 450 mm. Then, various physical properties of the graphitefilm were measured. The results of this measurement are shown in Tables1C and 2C.

Comparative Example 1C

In the same manner as that in Example 1C, the carbonization step and thegraphitization step were carried out. However, the wound film tighteningstep and the straightening-for-flatness process step were not carriedout. As a result, thus obtained graphite film had a sag Zgs of 120 mm, alength of 45.0 m, and a width of 450 mm. Then, various physicalproperties of the graphite film were measured. The results of thismeasurement are shown in Tables 1C and 2C.

Comparative Example 2C

A graphite film was produced in the same manner as that described inExample 1C, except that the maximum temperaturestraightening-for-flatness process step was set at 1800° C. As a result,thus obtained graphite film had a sag Zgs of 120 mm, a length of 45.0 m,and a width of 450 mm. Then, various physical properties of the graphitefilm were measured. The results of this measurement are shown in Tables1C and 2C.

Comparative Example 3C

A graphite film was produced in the same manner as that described inExample 1C, except that the inner core 1 employed in Comparative Example3C had a center circumference of 314.0000 mm and an end 1 circumferenceof 319.3380 mm, and an end 2 circumference of 319.3380 mm. As a result,thus obtained graphite film had a sag Zgs of 130 mm, a length of 45.0 m,and a width of 450 mm. Then, various physical properties of the graphitefilm were measured. The results of this measurement are shown in Tables1C and 2C.

TABLE 1C Conditions for Rewinding Step Raw Graphite Vertical FilmProperties Strength Winding Inner Core 1 Sag Thermal Sag of Tight or ZgsDiffusivity Length Zgs Torque Winding Lateral mm cm²/s m mm N · m N ·m/m Winding Type Material Example 1C 120 8.300 45 120 4 220 VerticalCylinder MSG Winding Example 2C 120 8.300 45 120 4 220 Vertical CylinderMSG Winding Example 3C 120 8.300 45 120 4 220 Vertical Cylinder MSGWinding Example 4C 120 8.300 45 120 4 220 Vertical Cylinder MSG WindingExample 5C 120 8.300 45 120 4 220 Vertical Cylinder MSG WindingComparative 120 8.300 45 120 Not Carried Out Example 1C Comparative 1208.300 45 120 4 220 Vertical Cylinder MSG Example 2C Winding Comparative120 8.300 45 120 4 220 Vertical Cylinder MSG Example 3C WindingConditions for Rewinding Step Vertically Inner Core 1 Placed LinearCenter End 1 End 2 Diameter Starting Max or Expansion CircumferenceCircumference Circumference Accuracy Temp Temp Transversely ×10⁻⁶/K mmmm mm % ° C. ° C. Placed Example 1C 4.00 314.0000 314.1338 314.13380.0426 23 2900 Transversely Placed Example 2C 4.00 314.0000 314.0336314.0336 0.0107 23 2900 Transversely Placed Example 3C 4.00 314.0000314.0085 314.0085 0.0027 23 2900 Transversely Placed Example 4C 4.00314.0000 314.0019 314.0019 0.0006 23 2900 Transversely Placed Example 5C4.00 314.0000 314.0000 314.0000 0.0000 23 2900 Transversely PlacedComparative Not Carried Out Example 1C Comparative 4.00 314.0000314.1338 314.1338 0.0426 23 1800 Transversely Example 2C PlacedComparative 4.00 314.0000 319.3380 319.3380 1.7000 23 2900 TransverselyExample 3C Placed

TABLE 2C Graphite Film Properties Inner Core 1 Thermal Sag Zgs LengthMIT Diffusivity Lamination to mm m Times cm²/s Copper Foil Example 1C 2045.0 >10000 8.5 C Example 2C 10 45.0 >10000 8.5 B Example 3C 545.0 >10000 8.5 A Example 4C 1 45.0 >10000 8.5 A Example 5C 0.145.0 >10000 8.5 A Comparative 120 45.0 >10000 8.3 E Example 1CComparative 120 45.0 >10000 8.3 E Example 2C Comparative 130 45.0 >100008.5 E Example 3C

<Effects of Straightening-for-Flatness Process Step>

As shown in Tables 1C and 2C, sag could not be controlled in ComparativeExample 1C where no straightening-for-flatness process was carried out.The graphite film obtained in Comparative Example 1C, had a sag Zgs of120 mm. On the other hand, in each of Examples 1C through 5C where thesag controlling step was carried out, the graphite film obtained wasexcellent in flatness and had a sag Zgs of not more than 20 mm. This isbecause the raw graphite film was pushed outward by the inner core inthe process of heat treatment due to difference in thermal expansioncoefficient between the inner core and the raw graphite film woundaround the inner core and thereby the film was flattened. Further, asdiameter accuracy of the inner core was increased, a sag Zgs becameshallower. Accordingly, in each of Examples 4C and 5C, a very flatgraphite film having a sag Zgs of not more than 1 mm could be obtained.On the other hand, in Comparative Example 3C where the inner core had apoor diameter accuracy of 1.7% in diameter, the graphite film obtainedhad a very deep sag, that is, a sag Zgs of 130 mm. The graphite film ofComparative Example 1C had many laminating wrinkles and had a very poorevaluation that was E in the evaluation of the lamination property tothe copper foil tape. On the other hand, the flat graphite films ofExamples 1C through 5C were excellent in the evaluation of thelamination property to the copper foil tape and each had an excellentevaluation that was C or higher. In particular, the flat graphite filmsof Examples 3C through 5C had very few laminating wrinkles and had anexcellent evaluation that was A.

<Maximum Temperature in Straightening-for-Flatness Process Step>

A comparison between Example 1C and Comparative Example 2C revealed thatwhen the maximum temperature in the straightening-for-flatness processstep was higher, sag could be controlled more. This result is becausethe higher maximum temperature of the straightening-for-flatness processstep results in larger difference in amount of expansion between theinner core and the raw graphite film wrapped around the inner core andthereby the graphite film was straightened more. The above result isobtained also because the higher temperature causes more activerealignment of graphite crystallites.

INDUSTRIAL APPLICABILITY

According to the present invention, it is possible to obtain a graphitefilm with controlled sagging or a graphite film excellent in flatness.The present invention is therefore applicable to, for example, materialsfor various electronic/electric apparatuses, including heat dissipationcomponents for dissipating heat from components that generate heat,e.g., for semiconductor elements mounted in various electronic orelectric apparatuses such as computers.

REFERENCE SIGNS LIST

-   11 Tears of graphite film-   21 Roll 1-   22 Roll 2-   23 Graphite film-   24 Suspended line-   25 Sag-   31 Widthwise direction of film-   32 Lengthwise direction of film-   33 Length of middle portion-   34 Length (W) of one of both ends-   35 Graphite film-   36 Length (E) of the other of both ends-   41 Graphite film having a sag in a middle portion-   42 Graphite film having no sag-   43 Graphite film having sags at both ends thereof-   44 Sag in middle portion-   45 Sag at ends-   46 Graphite film having sag at one end-   51 Middle portion-   52 Ends-   53 Temperature measurement point of end 1-   54 Temperature measurement point of middle portion-   55 Temperature measurement point of end 2-   56 Any widthwise direction-   61 Heat treatment apparatus-   62 Graphite weight-   63 Polymer film-   64 Graphite hearth-   65 Temperature measurement point-   71 Graphite cylindrical container-   81 Wind-off device-   82 Wind-up device-   91 Sag at an outer edge-   92 Sag at a point 30 mm away from the outer edge-   101 Sag in the middle portion-   111 Table-   112 Graphite film-   113 Positions of a ruler-   121 Graphite film-   122 Wind-off paper tube-   123 Wind-up paper tube-   124 Distance between both paper tubes-   131 Sheet having a self-adhesive layer or an adhesive layer-   132 Wind-off roll for the sheet having a self-adhesive layer or an    adhesive layer-   133 First roll-   134 Second roll-   135 Separator-   136 Wind-up roll for separator-   137 Bar as a trigger at which peeling of the separator is started-   138 PET tape with separator-   139 Width of the graphite film-   1310 Width of the sheet having a self-adhesive layer or an adhesive    layer-   141 Graphite film-   142 First roll-   143 Angle formed by a line connecting (the starting point of contact    between the first roll and the graphite film) and (the center point    of the first roll) and a line connecting (the center point of the    first roll) and (the point of contact between the first roll and the    second roll)-   144 Starting point of contact between the first roll and the    graphite film-   145 Center point of the first roll-   146 Point of contact between the first roll and the second roll-   151 Graphite composite film-   152 Enlarged view-   153 Laminating wrinkles-   161 Roll of a carbonized film-   162 Hearth-   163 Direction of gravitational force-   11′ Graphite film having been subjected to rolling-   12′ MD direction-   13′ Wrinkle-   151′ Graphite composite film-   152′ Enlarged view-   153′ Laminating wrinkles-   171 Angle b formed by a line connecting a starting point of contact    between the raw graphite film and an upper rolling-mill roll and a    center point of the upper rolling-mill roll and a line connecting    the center point of the upper rolling-mill roll and a point of    contact between the upper rolling-mill roll and a lower rolling-mill    roll.-   172 Starting point of contact between the upper rolling-mill roll    and a graphite film-   173 Center point of the upper rolling-mill roll-   174 Point of contact between the upper rolling-mill roll and the    lower rolling-mill roll-   175 Upper rolling-mill roll-   176 Lower rolling-mill roll-   177 Graphite film-   221 Graphite composite film-   222 Enlarged view-   223 Laminating wrinkles-   231 Winding deviation of graphite film-   241 Weight-   242 Raw graphite film-   243 Stage-   251 Room temperature-   252 During heat treatment-   253 Raw graphite film-   254 Inner core-   261 Stage-   262 Drive shaft-   263 Inner core-   264 Double-faced tape-   265 Raw graphite film-   266 Cross section after rewinding-   267 Outermost radius of roll of raw graphite film-   268 Center of the drive shaft-   269 Radius of the inner core-   2610 Winding thickness of raw graphite film-   271 Cylindrical inner core made of graphite-   272 External cylinder-   273 Polyimide film wrapped around the cylindrical inner core-   274 Apertures for ventilation-   281 Anchorage-   282 Carbonized film-   291 Roll 1-   292 Roll 2-   293 Polymer film-   294 Suspended line-   295 Sag-   296 Detachable shaft on which film is placed-   2111 Roll start-   2112 Roll end-   2121 Sheet having a self-adhesive layer or an adhesive layer-   2122 Wind-off roll for the sheet having a self-adhesive layer or an    adhesive layer-   2123 First roll-   2124 Second roll-   2125 Separator-   2126 Wind-up roll for separator-   2127 Bar as a trigger at which peeling of the separator is started-   2128 Copper foil tape with separator-   2129 Width of the graphite film-   21210 Width of the sheet having a self-adhesive layer or an adhesive    layer-   21211 Wind-off roll for graphite film-   21212 Graphite film-   2131 Tears-   2141 Raw graphite film-   2142 Graphite film having been subjected to the straightening    process-   2151 Structure 1-   2152 Structure 2-   2153 Structure 3-   2154 Structure 4-   2155 Structure 5-   2156 Structure 6-   2157 LED chip-   2158 Glass epoxy substrate-   2159 Metallic substrate-   21510 Graphite film-   2161 Expandable inner core-   2162 Raw graphite film-   2163 State after expanded-   2171 Jig having a small coefficient of thermal expansion-   2172 Jig having a large coefficient of thermal expansion-   2173 Carbonized film in sheet form

The invention claimed is:
 1. A method for producing a graphite film,comprising: a sag controlling step of controlling (i) temperatures of apolymer film at both widthwise ends and (ii) a temperature of thepolymer film in a widthwise middle portion within a temperature rangefrom a starting temperature of thermal decomposition of the polymer filmto a sag controlling temperature of the polymer film; and a step oftreating the film obtained in the sag controlling step with heat at atemperature of 2000° C. or higher after the sag controlling step,wherein the sag controlling step comprises treating the polymer filmwith heat so that the temperatures (i) are higher than the temperature(ii) within the temperature range from the starting temperature ofthermal decomposition of the polymer film to the sag controllingtemperature of the polymer film and so that a temperature gradient overan area extending from the both widthwise ends of the polymer filmtoward the widthwise middle portion of the polymer film is not less than2.5° C./m, and the film obtained in the sag controlling step is treatedwith heat at a temperature of 2000° C. or higher after the sagcontrolling step, and wherein the sag controlling step treats thepolymer film with heat under a condition that the temperature gradientover an area extending from the both widthwise ends of the polymer filmtoward the widthwise middle portion of the polymer film is not less than2.5° C./m and not more than 100° C./m.
 2. The method according to claim1, wherein in the sag controlling step, the polymer film is treated withheat while being moved through a heat treatment apparatus.
 3. The methodaccording to claim 1, wherein a temperature gradient over an areaextending from one of the both widthwise ends of the polymer film towardthe widthwise middle portion of the polymer film is identical to atemperature gradient over an area extending from the other of the bothwidthwise ends of the polymer film toward the widthwise middle portionof the polymer film.
 4. The method according to claim 1, wherein atemperature gradient over an area extending from one of the bothwidthwise ends of the polymer film toward the widthwise middle portionof the polymer film is different from a temperature gradient over anarea extending from the other of the both widthwise ends of the polymerfilm toward the widthwise middle portion of the polymer film.
 5. Themethod according to claim 1, wherein the sag controlling step treats thepolymer film with heat under a condition that the temperature gradientover the area extending from the both widthwise ends of the polymer filmtoward the widthwise middle portion of the polymer film is not less than10° C./m and not more than 50° C./m.
 6. The method according to claim 1,wherein the polymer film has a width in the range from 50 to 300 mm.